It could increase potential GDP (Gross Domestic Product) by 0.43% by 2050, a Frontier Economics study found, she said.
Ms Reeves said an expansion could create more than 100,000 jobs.
The announcement has been welcomed by some business groups but anger by London’s Labour mayor Sadiq Khan, the Lib Dems, the Green Party and environmental groups.
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As part of a speech on funding infrastructure across the UK to promote growth, Ms Reeves said: “Persistent delays have caused doubts about our seriousness towards improving our economic prospects.”
She added that business groups like the Confederation of British Industry (CBI), the Federation of Small Businesses (FSB) and the Chambers of Commerce (BCC), as well as trade unions “are clear – a third runway is badly needed”.
Ms Reeves said the UK is “already making great strides in transitioning to cleaner and greener aviation” and announced the government is investing £63m over the next year into the Advanced Fuel Fund grant programme to support the development of sustainable aviation fuel production plants.
The government will be accepting proposals until the summer and will then carry out a “full assessment” through the Airport National Policy Statement to “ensure a third runway is delivered in line with our legal, environmental and climate objectives”.
Ms Reeves said the government expects any associated surface transport costs to the third runway’s construction will be financed through private funding.
However, he said last week he would not resign if the government approved a third runway despite threatening to resign from Gordon Brown’s cabinet as climate change secretary in 2009 over the plans and in 2018 he said an expansion was “very likely” to make air pollution worse.
He has now said the government can meet both its growth and net zero missions together.
Labour Mayor of London Sadiq Khan said he remains opposed to a third runway “because of the severe impact it will have on noise, air pollution and meeting our climate change targets”.
He said he will carefully scrutinise any new proposals, “including the impact it will have on people living in the area and the huge knock-on effects for our transport infrastructure”.
“Despite the progress that’s been made in the aviation sector to make it more sustainable, I’m simply not convinced that you can have hundreds of thousands of additional flights at Heathrow every year without a hugely damaging impact on our environment,” he added.
Green Party MP Sian Berry said expanding airports “in the face of a climate emergency is the most irresponsible announcement from any government I have seen since the Liz Truss budget”.
Conservative shadow chancellor Mel Stride accused Ms Reeves and Sir Keir Starmer, and “their job destroying budget” of being “the biggest barriers to growth”.
“What’s worse, the anti-growth chancellor could not rule out coming back with yet more tax rises in March,” he added.
“This is a Labour government run by politicians who do not understand business, or where wealth comes from. Under new leadership, the Conservatives will continue to back businesses and hold this government to account.”
This breaking news story is being updated and more details will be published shortly.
Singer and actress Marianne Faithfull has died at the age of 78.
A spokesperson said: “It is with deep sadness that we announce the death of the singer, songwriter and actress Marianne Faithfull.
“Marianne passed away peacefully in London today, in the company of her loving family.
“She will be dearly missed.”
Faithfull was best known for her 60s hit As Tears Go By, written by The Rolling Stones’ Jagger and Keith Richards.
She also starred in films including The Girl on a Motorcycle and 2007’s Irina Palm, for which she was nominated for a European Film Award for Best Actress.
In recent years, she provided voice work for the 2021 remake of Dune and 2023’s Wild Summon.
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Born in 1946, Faithfull started her singing career in 1964 after being discovered by the Stones’ manager Andrew Loog Oldham.
Her self-titled debut album was released a year later, with As Tears Go By reaching number nine on the UK singles chart.
She went on to have a string of successful singles, including Come and Stay with Me, This Little Bird, and Summer Nights, and famously dated Sir Mick from 1966 to 1970.
Faithfull was prolific throughout the 60s, releasing six albums – some only in the UK and some for the US – as well as contributing backing vocals to the Beatles’ Yellow Submarine and inspiring the Stones’ Sympathy For The Devil.
That decade also saw her star in films like 1967’s I’ll Never Forget What’s’isname – where she was one of the first people to say f*** in a mainstream studio film – 1968’s The Girl on a Motorcycle, and Tony Richardson’s 1969 adaptation of Hamlet.
Her relationship with Sir Mick was notorious, with the couple being arrested in 1968 for possession of cannabis.
She was also infamously found by police wearing only a bear skin rug when they arrived for a drugs raid at Richard’s home in 1967.
After breaking up with the Stones frontman, Faithfull spent two years homeless in Soho while suffering from anorexia and heroin addiction, before she started living in a squat.
She wrote in her 1994 autobiography: “For me, being a junkie was an admirable life. It was total anonymity, something I hadn’t known since I was 17.
“As a street addict in London, I finally found it. I had no telephone, no address.”
In 1979, following success in Ireland with the country-themed Dreamin’ My Dreams, Faithfull released the Grammy-nominated Broken English – widely considered her best album.
She later achieved critical acclaim as a jazz and blues singer with 1987’s Strange Weather and went to rehab that same decade.
Faithfull released a total of 21 solo albums throughout her career. Her most recent was the spoken word album She Walks in Beauty from 2021, which saw her work with frequent Nick Cave collaborator Warren Ellis.
She made a full recovery from breast cancer in 2006, and fell into a coma after catching COVID-19 early in 2020 before recovering.
The winner, who chose to remain anonymous, scooped the third-biggest National Lottery winner ever.
The biggest EuroMillions win by UK players was in 2022 when a single ticket-holder won £195m.
Two months before that, Joe and Jess Thwaite, from Gloucester, won a then record-breaking £184,262,899 with a Lucky Dip ticket for the draw in May 2022.
A man has been jailed after his XL bully attacked a 12-year-old girl.
Justin Allison, 38, from Ebbw Vale, was sentenced to three years in prison at Newport Crown Court on Wednesday.
The girl was seriously injured and needed hospital treatment, police said.
Allison had previously pleaded guilty to possessing a banned breed without a licence and being in charge of a dog dangerously out of control in a public place. He also admitted a charge of possessing an offensive weapon in a private place.
Officers were called to an address in Nantyglo, Blaenau Gwent, last October to reports a child had been attacked by a dog.
Gwent Police said the dog – later identified as an XL bully – was seized and humanely destroyed by a vet.
The breed was banned in England and Wales from 1 February last year, with the ban later extended to Scotland.
Detective Chief Inspector Virginia Davies said the girl was “viciously attacked” after Allison “failed to keep his dog under control”.
She said the case “should serve as a reminder to all dog owners of the importance of having your dog under control at all times”.
“We take all reports of suspected irresponsible dog ownership seriously and we urge everyone to follow the legislation and guidance to prevent events like this happening in the future,” she added.
Allison was also banned from owning dogs for 10 years.