In at least two respects – one expected, the other not – this was a historic budget.

The bit no one expected came just before midday. Normally on budget day, the documents containing all the measures and the official forecasts from the Office for Budget Responsibility (OBR) are published online when the chancellor has finished her speech.

The minute she sits down in the House of Commons, traders, journalists and economists around the country start frantically refreshing their browsers, hoping for first sight of this critical document.

It’s critical because often there is a striking gap between what the chancellor says in her speech and the details inside the document.

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Take, for instance, one of the chief money-raising measures in this year’s budget: the decision to limit the amount of money people can put into salary sacrifice schemes – something that affects most private sector pensions.

To judge from the chancellor’s speech alone, you might have thought this was a somewhat minor move designed to close a loophole used mostly by wealthy people. But the document shows that, on the contrary, this is a massive tax-raising measure that will bring in a whopping £4.7bn the first year it’s properly instituted.

That is a lot of money – a lot. And whenever the government raises those kinds of sums it invariably means a lot of people will end up paying quite a bit more money in tax. So you see the point: it’s only when you get the final document that you can see the grisly details in black and white.

And those details are more than academic. The contours of the numbers contained in the OBR’s Economic and Fiscal Outlook (EFO) – to give it its proper name – are enormously market-sensitive. They are sometimes the evidence base upon which gilt traders decide whether or not to invest in UK securities.

All of which helps explain why, when the OBR accidentally published its EFO online, nearly an hour before the chancellor stood up to deliver her speech, it caused an extraordinary flurry in markets.

The cost of government debt yo-yoed dramatically as investors hurriedly downloaded the documents and tried to work out what this budget meant for the UK economy.

This was the biggest budget leak in history and doubtless we will hear more in the coming weeks about how it happened and about the consequences. But, as I said at the start, it was not the only historic thing about this budget.

Because it also commits the government to a set of economic policies that take Britain into uncharted territory. The total level of taxation in the UK was already high before this budget – indeed, it was already heading up to the highest level in at least 70 years (actually it’s really the highest level ever – it’s just that the numbers only go back to the 1940s). But this budget supercharges the rise.

As a result of the policies contained in it, as well as the ones in last year’s budget, this parliament is, according to the Institute for Fiscal Studies, heading towards being the biggest tax-raising Parliament in modern history (the numbers in this case only go back to 1970).

Those higher taxes were, the chancellor judged, necessary for two reasons. First, they help her meet her fiscal rules, which in turn means investors begin to charge Britain less to borrow. And the early signs on this were promising: the yield on UK government debt dropped in the hours after that initial OBR-fuelled roller-coaster.

Second, they give her enough money to finance extra spending, much of which is going into extra welfare, in part to fund the abolition of the two child benefit cap. In short, this government is taxing more to spend more.

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That raises at least two questions. First, how successful will it actually be in raising those taxes? After all, Britain has never been as highly taxed as it will be at the end of this decade. Will Britons be content to become a high tax economy – like many of our European neighbours – or is the government being too sanguine about what this will mean for growth and, more to the point, its coffers.

Second, having spent much of its first 18 months trying and failing to control welfare spending – forced along the way into U-turns over its plans – can it really be depended on to keep to its expenditure plans off into the future?

The short answer is: no-one really knows. But now that the flurry of excitement over that historic leak is over, this big budget will be thoroughly scrutinised and thoroughly tested in the coming weeks and months.

Chancellor Rachel Reeves has unveiled the long-anticipated budget.

It comes after a report from the Office for Budget Responsibility (OBR), which analyses policies decided on by the chancellor, was published early in error.

Here are the key points:

Tax thresholds will be frozen for an additional three years from 2028

The point at which people start paying higher rates of tax will be held. It can mean earners will be dragged into higher tax bands when they get a pay rise.

This will raise £8bn.

Taxes hiked on gambling

The gambling industry is going to be taxed more, to raise more than £1bn.

Remote gaming duty will rise to 40% from 21% while online betting tax will rise from 15% to 25%.

The bingo tax is being abolished from April.

New mileage-tax on electric cars

Electric car drivers will be subject to a 3p charge for every mile they drive.

Plug-in hybrid vehicles will be charged 1.5p per-mile.

This is expected to raise £1.4bn, according to the OBR report.

Change to capital gains tax for employee ownership trusts

Capital gains tax relief on business sales made to employee ownership trusts will be reduced from 100% to 50%.

This is expected to raise £900m.

Other tax hikes

The tax paid on dividends – payments to shareholders – as well as property and savings income will rise 2 percentage points, raising £2.1bn.

Two-child benefit cap scrapped

The government will scrap the two-child benefit cap from April 2026.

This currently limits the amount of benefits parents can claim for their third child or subsequent children who were born after 6 April 2017.

By scrapping the cap, the government hopes an estimated 450,000 children will be lifted out of poverty.

According to the OBR’s analysis of the chancellor’s budget this will cost the government £2.3bn.

Salary-sacrifice pension contributions above £2,000 to face national insurance

From April 2029, national insurance will be charged on salary-sacrificed pension contributions above an annual £2,000 threshold.

This will raise £4.7bn and will come into effect in 2029.

State pension increases

There’ll be an increase of £440 per year for the basic state pension and an increase of £575 per year for the new state pension.

Reforms for cash ISAs

Savers will only be able to put up to £12,000 into cash ISAs tax-free each year. This is reduced from £20,000 in the hopes that Britons will instead put their money into stocks and shares ISAs.

Over 65s can retain the full £20,000 allowance.

Fuel duty to be frozen until next September

The duty, or tax, paid on diesel and petrol has been frozen at 52.95p per litre.

This will cost the government £2.4bn next year and £900m each year after.

Mansion tax introduced on properties worth more than £2m

It means the most expensive properties in the country, worth more than £2m, will have to pay extra. This will be £2,500 for properties worth £2m to £2.5m and up to £7,500 for homes valued at £5m.

This will raise £400m, the OBR has confirmed.

Cut in energy bills

The average annual energy bill will be cut £150 from April by reducing levies.

The Energy Company Obligation (ECO) scheme, which is designed to tackle fuel poverty and help reduce carbon emissions, will be scrapped.

Luxury cars removed from the Motability scheme

This scheme, which provides subsidies for people with a disability to lease a vehicle, is part of PIP.

Freeze on student loan repayment rate

The student loan repayment threshold will be maintained for three years.

Training for apprentices under-25 free at small companies

A new Youth Guarantee will give £820m towards tyring to guarantee every young person a place in college, an apprenticeship or personalised job support.

After 18 months, 18-to-21 year-olds will be offered paid work instead of benefits.

Wider inheritance tax rules

A change to inheritance tax will allow the transfer of 100% relief allowance between spouses.

Uber and Bolt journeys to be taxed

Journeys taken on ride-hailing apps such as Uber and Bolt will be subject to tax in a measure being described as a taxi tax.

Rail fares frozen

Rail fares will be frozen for the first time in 30 years, with passengers not paying any more for season tickets, peak return and off-peak return tickets between major cities.

Business rate changes

Business rates will be reduced for 750,000 retail, hospitality and leisure properties, which will be funded by an increase on premises worth more than £500,000.

The tax reduction will be paid for by an increase in taxes on properties worth £500,000 or more, like the warehouses used by online giants.

Stamp duty break for companies new to London Stock Exchange

A stamp duty holiday for companies newly listing on the London Stock Exchange will be in place for three years.

OBR forecast

Next year, economic growth is expected to be lower than the OBR thought in March. GDP will be 1.4% in 2026, down from a previously anticipated 1.9%.

It will be 1.5% for the rest of the decade.

According to the independent forecasters, prices are expected to rise faster than the OBR thought in March due to higher wages and food costs.

Inflation will be 3.5% this year and 2.5% next.

The amount of fiscal headroom the chancellor has doubled to £22bn in 2029-30. This means a £22bn financial cushion against price shocks such as the COVID-19 pandemic and soaring energy costs.

NHS technology and new neighbourhood health centres

The government will invest £300m in NHS technology and 250 new neighbourhood health centres with the aim to expand more services into communities.

Over 100 centres, including in Birmingham, Truro and Southall, are expected to be delivered by 2030.

Prescription costs frozen

The cost of an NHS prescription in England will be frozen at £9.90.

2.6% of GDP to be spent on defence

The government will spend 2.6% of GDP, a measure of everything produced in the economy, on defence.

National wage increases

From next April, the national living wage will rise by 4.1% to £12.71 an hour for eligible workers aged 21 and over.

The national minimum wage rate for 18 to 20-year-olds will increase by 8.5% to £10.85 an hour.

For 16 to 17-year-olds and those on apprenticeships, the national minimum wage will increase by 6% to £8 an hour.

Nations and local mayors

The government of Northern Ireland government will get an additional £317m, £505m for the Welsh government and £820m for the Scottish government.

“Flexible” funding worth £13bn has been pledged for seven regional mayors to invest in skills, business support and infrastructure.

The owner of Candy Kittens, the vegetarian sweet brand, is in talks about a cut-price deal to buy Graze, the snacks range owned by FTSE-100 consumer goods giant Unilever.

Sky News has learnt that Katjes Group, which is headquartered in Germany, is in advanced talks to buy Graze for about £35m.

The price represents a huge discount on the roughly £150m Unilever paid to buy the healthy snacks brand in 2019.

Graze’s products, which are sold in major supermarkets and also through subscriptions directly to consumers, include espresso-flavoured almonds and honeycomb oat bars.

Founded in 2008, Graze was bought by Unilever after it saw off interest from competing bidders including Kellogg and Pepsico, the owner of Walkers Crisps.

The brand has performed poorly under Unilever’s ownership, however, prompting new chief executive Fernando Fernandez to put it up for sale earlier this year.

Nevertheless, the sale price of about £35m is lower than market estimates suggested earlier this year.

Mr Fernandez has also initiated a sale process for prominent British food brands including Colman’s, Bovril and Marmite, according to reports last week.

The new Unilever boss is prioritising investments in faster-growing areas in consumer healthcare and beauty, snapping up the personal care brand Wild earlier this year.

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A Unilever spokesman declined to comment.