Campaigners have called for government “transparency” amid reports the United States Air Force has moved nuclear weapons to a Suffolk airbase.

Flight data showed a specialist C-17A Globemaster transporter – capable of carrying extra heavy loads – travelling more than 4,400 miles (8,200km) from New Mexico in the United States to RAF Lakenheath last week.

The Campaign for Nuclear Disarmament (CND) said Prime Minister Keir Starmer should “come clean” and make a formal statement about the potential deployment.

Neither the United States Air Force (USAF) or the Ministry of Defence comments on nuclear weapons deployments.

Last year, the US Department of Defence indicated RAF Lakenheath was preparing facilities to house and guard nuclear bombs.

Documents detailing a contract awarded to build defensive shelters for the base’s “upcoming nuclear mission” were published, and then withdrawn.

It would be the first time since 2008 that nuclear weapons had been in place at Lakenheath.

The base is home to the 48th Fighter Wing, also known as the Liberty Wing.

The F-35A Lightning II jets stationed at the base have successfully been flight tested to carry the short-range B61-12 thermonuclear bomb, a tactical weapon designed for the battlefield.

William Alberque, a former NATO arms control expert, said he believed the transporter’s cargo included B61-12 nuclear bombs.

Mr Alberque, who is now at the foreign policy research institute The Pacific Forum, said all signs pointed to the aircraft carrying nuclear weapons.

“One would have to say the balance of evidence has tipped the scales from ‘no’ to ‘yes’.

“We know the C-17s loaded at a ‘hot weapons’ pad because their transponders were on – and that this is voluntary and often not done.”

The transponder’s code was for a dangerous load, he told the BBC, and that air refuelling had taken place over the Atlantic.

“If they had no nuclear cargo, they could have refuelled on the ground,” he said, adding “that’s a message”.

Suffolk-based aviation analyst Roger Smith agreed the indications were the plane was carrying a nuclear payload.

The C-17A originally took off from its base at McChord Air Force Base in Washington State on 15 July before going to USAF’s Nuclear Weapons Center at Kirtland Air Force Base, according to data from the flight tracking website ADS-B Exchange.

He said it used the callsign REACH 4574, which is primarily used by the US Air Mobility Command.

He told the BBC the four digit number indicated a more specialised or sensitive mission and that the callsign is also associated with the Prime Nuclear Airlift Force (PNAF) based at McChord AFB.

“The PNAF is a group of specialist aircrew and loading crews, trained and cleared to move nuclear weapons by air” he added.

Reacting to the reports of the possible delivery of the bombs, the Campaign for Nuclear Disarmament (CND) called on the prime minister to make a formal statement.

Chairman Tom Unterrainer said: “It is completely inappropriate for the public to be finding out about such a major escalation in nuclear dangers via reports in British newspapers and the assessments of security experts.

“Keir Starmer must make a public statement about this major change in Britain’s security arrangements and allow for a transparent and democratic debate on this to be held in Parliament.”

A Ministry of Defence spokesman said: “It remains a long-standing UK and NATO policy to neither confirm nor deny the presence of nuclear weapons at a given location.”

A US Department of Defense official said: “Consistent with longstanding US policy, we neither confirm nor deny the presence or absence of nuclear weapons at any particular location.”