LONDON — The British government has confirmed it is developing a new nuclear warhead for its missile submarines, days after the U.S. revealed the program was going ahead before Parliament had been informed.

In a written statement to Parliament, Defence Secretary Ben Wallace confirmed Feb. 25 that Britain is working on a new warhead to equip it’s Trident missile-armed nuclear submarine fleet.

“To ensure the Government maintains an effective deterrent throughout the commission of the Dreadnought Class ballistic missile submarine we are replacing our existing nuclear warhead to respond to future threats and the security environment,” Wallace said.

The announcement was not expected to be made prior to publication of the defense, security and foreign policy review scheduled for late this year. But the Conservative government’s hand was forced when U.S. officials revealed last week the program was up and running.

That caused a stir in the U.K., as high-profile programs like the nuclear deterrent are usually announced in Parliament first. It’s only a courtesy, but if Parliament is not informed first, ministers can be forced to attend the House of Commons to make a statement.

“The decision is basically a forgone conclusion, but the announcement has come sooner than expected. We were looking at probably next year but certainly not before the defense and security review due for release towards the end of the year,” said David Cullen , the director at the U.K.-based Nuclear Information Service, an independent organization promoting awareness of nuclear weapons issues.

Adm. Charles Richard, commander of U.S. Strategic Command, and Alan Shaffer, the Pentagon’s deputy undersecretary of defense for acquisition and sustainment, separately made statements that Britain is pursuing development of its own version of the W93 warhead, which is in the assessment phase for the U.S. military ahead of replacing U.S. Navy W76 warhead.

“It’s wonderful that the U.K. is working on a new warhead at the same time, and I think we will have discussions and be able to share technologies,” Shaffer told an audience at the Nuclear Deterrence Summit, hosted in Washington by ExchangeMonitor.

Shaffer said the W93 and the British weapon “will be two independent development systems.”

Richard, in testimony prepared for the Senate Armed Services Committee, said Feb. 20 that the W93 will “support a parallel replacement warhead program in the United Kingdom.”

Wallace told Parliament that the Defence Ministry’s “Defence Nuclear Organisation is working with the Atomic Weapons Establishment: to build the highly skilled teams and put in place the facilities and capabilities needed to deliver the replacement warhead; whilst also sustaining the current warhead until it is withdrawn from service. We will continue to work closely with the US to ensure our warhead remains compatible with the Trident.”

The new British warhead will replace the existing weapon, known as the Trident Holbrook, which equips the four Vanguard-class submarines charged with providing Britain’s nuclear deterrence capability.

Cullen noted that the existing British weapon is unlikely to be very different from America’s W76.

“They are both fitted to the same Trident missile used by Britain and the U.S. Our assumption is the two warheads are very close, if not virtually identical," he said.

The Atomic Weapons Establishment in the U.K. is undertaking a life-extension program on its stock of warheads, including replacing some electronics and systems to improve accuracy and provide performance benefits.

The Trident Holbrook entered service along with the Vanguard-class submarines in the mid-1990s. Britain plans to replace the subs in the early 2030s with four new Dreadnought-class subs. Work on the £31 billion (U.S. $40 billion) boat program is already underway.

Britain is also spending billions of pounds building infrastructure to support the Atomic Weapons Establishment’s development, building and testing of a new warhead at sites in southern England and Valduc, France, where Britain is cooperating in hydrodynamic experiments with the French Alternative Energies and Atomic Energy Commission as part of a wider nuclear agreement.

Cullen said there is little in the public domain on the delivery timetable for the current warhead updates.

“They started delivery of the life-extended warheads around 2016/2017. The warheads will last up to another 30 years if you assume they are doing similar changes to updates being undertaken by the U.S.,” he said. “I expect Mk4A, [as the updated weapon is referred to], to come out of service in the mid-2040s with the replacement warhead being available from the late 2030s at the earliest.”

Britain and the U.S. have cooperated on nuclear weapons development for decades. In 1958, they signed what is known as the Mutual Defence Agreement to formalize that arrangement. That pact remains in place and is renewed about every decade. It was last signed in 2014.