The government's sale of its remaining holdings in nuclear deterrent Trident to a private US firm has prompted criticism from opposition parties.
State-owned nuclear firm British Nuclear Fuels (BNFL) said its stake in the Atomic Weapons Establishment (AWE) programme in Aldermaston, which is responsible for the country's nuclear deterrent Trident, had been purchased by the Jacobs Engineering Group.
The other two-thirds of the firm are held by American defence firm Lockheed Martin and the British company Serco, meaning that the state no longer owns the programme which produces and maintains the country's nuclear weapons.
Opposition MPs have expressed concern over the move with the Liberal Democrats asking how it had been allowed without parliamentary oversight.
Liberal Democrat defence spokesman Nick Harvey said: "It is staggering that the government could do something of such strategic importance without informing parliament."
He added: "The whole argument used for Britain having a separate weapons establishment is that this is required by the [nuclear] non-proliferation treaty, as technology-sharing is not allowed. We must therefore query the rationale of a US company having a majority shareholding in AWE.
"There has always seemed to be a lot of cloak and dagger around Aldermaston, and now it appears the government has concealed something of huge significance from parliament. If the company has declared the deal is going ahead to the New York Stock Exchange, they must be fairly sure this is the case."
The Conservatives have called for the government to provide an explanation about the deal.
A Ministry of Defence spokesman said: "It is the UK government, not AWE, that sets the UK's nuclear policy.
"UK sovereign interests remain protected at all times, as does the independence of the UK deterrent. The safe operation of AWE will remain unaffected by the sale."