Donald Trump’s steel and aluminium tariffs have come into effect.

But what are they and what do they mean for the UK?

What are tariffs and why does Trump want to impose them?

Tariffs are taxes on goods imported into the US.

The US president wants to impose wide-ranging tariffs on nearest neighbours Mexico and Canada, which he says will help reduce illegal migration and the smuggling of the synthetic opioid fentanyl to the US.

However, most of the 25% duties imposed on the pair to date have been suspended until 2 April.

But two rounds of tariffs on China have been enacted – reflecting trade imbalances and Mr Trump’s battle against fentanyl.

So why is he now targeting steel and aluminium?

On Wednesday, a separate 25% tariff on all steel and aluminium imports to the US came into effect, affecting UK products worth hundreds of millions of pounds.

The steel and aluminium tariffs are designed to protect US manufacturing and bolster jobs by making foreign-made products less attractive.

The world’s largest economy relies on imports of steel and aluminium and Mr Trump wants to change that.

How have countries – including the UK – reacted?

The European Union has announced it will impose retaliatory tariffs on the US.

The European Commission said it will impose “countermeasures” affecting €26bn (£21.9bn) of US goods from 1 April after US tariffs on steel and aluminium came into force today.

The bloc’s tariffs will not only impact US steel and aluminium products, but also textiles, home appliances and agricultural goods.

Canada has announced 25% retaliatory tariffs on US goods worth C$29.8bn (£16bn) from tomorrow, its country’s finance minister has said.

The tariffs will include steel products worth C$12.6bn (£6.8bn) and aluminium products worth C$3bn (£1.6bn).

Computers, sports equipment and cast iron goods are also among the other products subject to the new retaliatory tariffs.

Announcing the tariffs, Canada’s foreign minister, Melanie Joly, added that Canada will raise the issues of tariffs with European allies to coordinate a response to put pressure on the US.

While UK industry sees it as a direct attack, the reality is that this country is not a major player any more because energy costs, in particular, mean that UK-produced steel is expensive.

Nevertheless, stainless steel and some high-end products from the UK are in high demand and account for the bulk of the £350m in annual exports to the US.

Sir Keir Starmer has said he is “disappointed” to see Mr Trump impose global tariffs on steel and aluminium, saying the UK will take a “pragmatic approach” and “all options are on the table”.

The business secretary Jonathan Reynolds said on Wednesday morning that while he was disappointed, there would be no immediate retaliation by the UK government as negotiations continue over a wider trade deal with the US.

Why will metal products become more expensive?

It stands to reason that if you slap additional costs on importers in the US, that cost will be passed on down the supply chain to the end user.

If the aluminium to make soft drinks cans costs 25% more, for example, then the hit will have to be felt somewhere.

It could mean that any US product involving steel or aluminium goes up in price, but hikes could be limited if companies decide to take some of the burden in their bottom lines.

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What are the prospects for higher prices?

It depends on the extent to which costs are passed down through the supply chain as new tariff regimes and any reciprocal tariffs are deployed.

We do know that Mr Trump plans to fully roll out duties, on all goods, against Mexico and Canada from 2 April. But the White House did row back on a threat to double Canada’s tariff on its steel and aluminium – the biggest exporter – to 50%.

But Mr Trump is also widely expected to target almost all imports from the European Union from the beginning of April.

Is the UK facing further tariffs?

Mr Trump has not explicitly said that the UK is in his sights.

Data shows no great trade imbalances – the gap between what you import and export from a certain country – and UK figures show no trade deficit with the United States.

UK ministers have previously suggested this could be good news for avoiding new levies.

Why tariffs could cost you – even if Trump spares UK

Even if no tariffs are put on all UK exports to the US, consumers globally will still be impacted by the wider trade war, particularly in the US.

Economists believe that tariffs will raise costs in the US, sparking a wave of inflation that will keep interest rates higher for longer. The US central bank, the Federal Reserve, is mandated to act to bring inflation down.

More expensive borrowing and costlier goods and services could bring about an economic downturn in the US and have knock-on effects in the UK.

Forecasts from the National Institute of Economic and Social Research (NIESR) predict lower UK economic growth due to higher global interest rates.

It has estimated that UK GDP (a measure of everything produced in the economy) could be between 2.5% and 3% lower over five years and 0.7% lower this year.

The Centre for Inclusive Trade Policy thinktank said a 20% across-the-board tariff, impacting the UK, could lead to a £22bn reduction in the UK’s US exports, with the hardest-hit sectors including fishing and mining.