The budget of the Aldermaston Atomic Weapons Establishment (AWE) has been increased by £130m to £493m in a single year, in the biggest outlay of cash on the facility for several decades.

The government has also confirmed that it wants to boost the number of specialist scientists working at the Reading facility by more than a third over the next three years.

The huge increase in activity at Aldermaston comes as the government prepares to make a decision on whether to replace Britain's ageing Trident nuclear deterrent, which has to be taken by the end of the decade.

But opposition MPs and anti-nuclear campaigners last night claimed the massive influx of cash and personnel proved the government was already pressing ahead with work on alternative systems - and even warheads - despite an assurance that it was in the early stages of research.

Scotland on Sunday revealed two years ago that Britain was considering abandoning its long-range nuclear missiles in favour of cheaper "mini-nukes" that could be used to strike rogue states.

Ministry of Defence chiefs and ministers are understood to be in advanced negotiations with the United States over developing a new range of much smaller and cheaper "bunker-busting" nuclear weapons that could be used to launch first-strike attacks on enemies.

Ministers have consistently denied that they have already decided to replace the Trident warheads, carried on four submarines based at Faslane, on the Clyde. Maintaining Britain's independent nuclear weapons swallows up to 3% of the MoD's budget, about £1bn a year.

Ministers maintain that the increased budget at Aldermaston is required to maintain the safety of Britain's existing stockpile of nuclear weapons.

But Nick Harvey, Liberal Democrat defence spokesman, argues there is a more sinister motive.

He said: "There is a conspicuous recruitment drive, which would indicate that they are clearly doing some work on a new nuclear warhead."

The government has endorsed a £1bn package to upgrade facilities at Aldermaston, centring on the construction of the Orion laser, which will simulate conditions "found at the centre of a star or within a nuclear detonation".

Experts maintain that the improvements will enable scientists to estimate how new nuclear weapons would perform, without having to detonate one.

But Britain is also believed to be working closely with the United States on options for replacing the submarine-borne Trident warheads, which are expected to reach the end of their lives in 2025. Hundreds of British nuclear scientists have visited a series of nuclear weapons laboratories, including the Los Alamos complex.

Former defence secretary John Reid last month admitted: "Initial preparatory work is being undertaken by officials on possible options for the future of the UK's nuclear deterrent."

But he added: "Ministers have not yet begun to consider the position on this issue in any detail."

His successor, Des Browne, responded to challenges over the increased activity at Aldermaston by insisting that "hydrodynamics testing is essential in underwriting the safety and reliability of the existing stockpile without recourse to nuclear testing".

He also claimed Aldermaston was not developing a new nuclear weapon.

But Frank Barnaby, a nuclear physicist who advises the Oxford Research Group, said the increased activity clearly pointed to an advanced programme of work to replace Trident.

He said: "If Aldermaston is recruiting these bright young scientists it will have to give them something to do to keep them busy."

Barnaby, who used to work at Aldermaston, told Scotland on Sunday: "The scientists might put forward some alternatives, but all in all it suggests that the government has already gone some way down this road."

Related topics

• Faslane
  
• Nuclear defence