The UK is concerned that the proposed US anti-terror legislation – which was vetoed by President Barack Obama but could be overridden by the Congress – would leave its military and intelligence personnel at risk of being prosecuted in American courts and hostile states. Downing Street officials confirmed that the government has conveyed its concerns to their counterparts in Washington.

Security officials reportedly fear that the legislation, named the Justice Against Sponsors of Terrorism Act (Jasta), would empower hostile nations to take legal action against the US and its allies, including the UK. British intelligence and security agencies, MI6 and MI5 have also expressed similar concerns.

Keeping the implications of the bill in mind, Obama was prompted to block the proposal in a last-minute veto last week. But Congress is said to be gearing up to override the veto through a vote scheduled by the month-end.

If passed, the legislation – which is also called the 9/11 bill – would enable families of victims of the deadly 11 September 2001 tragedy to sue the Saudi Arabian government over its alleged links with the perpetrators of the attacks.

"No matter how well-intentioned this legislation might be, if it goes ahead it could pose a real threat to British personnel working in the military and the intelligence and security services," a senior Whitehall security official was quoted by The Telegraph as saying.

"Any attempt to interfere with the internationally-recognised laws concerning sovereign immunity could result in the military and intelligence services receiving an avalanche of vexatious litigation from hostile regimes," the source added.

A Downing Street official reportedly told the paper on Sunday (25 September) that the British government had "shared our concerns with [US officials] over the potential implications of the JASTA bill for international law, specifically the principles of state sovereignty and immunity".

The European Union has already raised similar concerns and has lodged a formal complaint with the US State Department over the proposed legislation.

The UK is concerned that the US's 9/11 bill, if passed, by the Congress despite President Barack Obama vetoing it, could make British military and intelligence personnel vulnerable to prosecution in US courts or by hostile nations - File photo Spencer Platt/ Getty Images