Inside Britain's largest nuclear weapons site - as scientists race to build a new warhead by the 2030s

Vaults of enriched uranium and plutonium to make nuclear bombs are dotted about a secure site in Berkshire along with Anglo-Saxon burial mounds and a couple of lakes.

Surrounded by metal fences topped with barbed wire, much of the nuclear weapons facility at Aldermaston in Berkshire looks frozen in time from the 1950s rather than ready for war in the 21st century.

But a renewed focus on the importance of the UK's nuclear deterrent means the government is giving much of its nuclear infrastructure a facelift as it races to build a new warhead by the 2030s when the old stock goes out of service.

Sky News was among a group of news organisations given rare access to the largest of Britain's nuclear weapons locations run by AWE.

The acronym stands for Atomic Weapons Establishment - but a member of staff organising the visit told me that the public body, which is owned by the Ministry of Defence, no longer attributes the letters that make up its name to those words.

"We are just A, W, E," she said.

She did not explain why.

Perhaps it is to avoid making AWE's purpose so immediately obvious to anyone interested in applying for a job but not so keen on weapons of mass destruction.

For the scientists and engineers, working here though, there seems to be a sense of genuine purpose as they develop and ensure the viability and credibility of the warheads at the heart of the UK's nuclear deterrent, this country's ultimate security guarantee.

"It's nice to wake up every day and work on something that actually matters," said a 22-year-old apprentice called Chris.

Sky News was asked not to publish his surname for security reasons.

The workforce at AWE is expanding fast, with 1,500 new people joining over the past year.

The organisation has some 9,500 employees in total, including about 7,000 at Aldermaston, where the warhead is developed and its component parts are manufactured.

Designing and building a bomb is something the UK has not needed to do for decades - not since an international prohibition on testing nuclear weapons came into force in the 1990s.

It means the new warhead, called Astrea, will not be detonated for real unless it is used - an outcome that would only ever happen in the most extreme of circumstances as explained in a new podcast series by Sky News and Tortoise called The Wargame.

The last time, Britain test-fired a bomb was at a facility in Nevada in the US in 1991.

With that no longer an option, the scientists at AWE must rely on old data and new technology as they build the next generation of warhead.

This includes input from a supercomputer at the Aldermaston site that uses 17 megawatts of power and crunches four trillion calculations per second.

Another major help is a giant laser facility.

It is built in a hall, with two banks of long cylinders, lying horizontal and stacked one of top of the other running down the length of the room - these are part of the laser.

The beams are then zapped in a special, separate chamber, onto tiny samples of material to see how they react under the kind of extreme pressures and temperatures that would be caused in a nuclear explosion.

The heat is up to 10 million degrees - the same as the outer edge of the sun.

"You take all those beams at a billionth of a second, bring them altogether and heat a small target to those temperatures and pressures," one scientist said, as he explained the process to John Healey, the defence secretary, who visited the site on Thursday.

Looking impressed, Mr Healey replied: "For a non-scientist that is hard to follow let alone comprehend."

The Orion laser facility is the only one of its kind in the world, though the US - which has a uniquely close relationship with the UK over their nuclear weapons - has similar capabilities.

Maria Dawes, the director of science at AWE, said there is a sense of urgency at the organisation about the need to develop and then build the new bomb - which is a central part of the government's new defence review published in early June.

"You've probably read the strategic defence review," she said.

"There's very much the rhetoric of this is a new era of threat and therefore it's a new era for defence and AWE is absolutely at the heart of that and so a sense of urgency around: we need to step up and we need to make sure that we've got what our customer needs. Yes, there's very much that sense here."

It means an organisation that has for years been purely focused on ensuring the current stockpile of warheads is safe and works must shift to becoming more dynamic as it pursues a project that will be used to defend the UK long into the future.

In a sign of its importance, the government is spending £15bn over the next four years alone on the programme to build the new warheads.

Part of the investment is going into revamping Aldermaston.

Driving around the 700-acre site, which was once a Second World War airbase, many of the buildings were constructed into the 1950s, 1960s and 1970s.

The construction of new science and research laboratories is taking place.

But bringing builders onto one of the UK's most secure nuclear sites is not without risk.

Everyone involved must be a British national and armed police patrols are everywhere.

No one would say what will be different about the new bomb that is being developed here compared with the version that needs replacing.

One official simply said the incumbent stock has a finite design life and will need to be swapped out.

(c) Sky News 2025: Inside Britain's largest nuclear weapons site - as scientists race to build a new warhead