Russian submarines are likely to have gathered "valuable intelligence" on Britain's nuclear deterrent since the Government scrapped maritime patrol aircraft, senior RAF figures have warned.
The UK's lack of submarine-hunting planes following the decision to axe the Nimrod fleet has given opportunities for "intruders" which could "prejudice the security and effectiveness" of Trident, they said.
In a letter to the Daily Telegraph, the five retired senior officers wrote: "The need to reintroduce Maritime Patrol Aircraft (MPA) into the British frontline is now widely recognised.
"With so few naval escorts available, this will be vital if future aircraft carriers are not to be put severely at risk.
"We know that Russian submarines are monitoring the area from which our nuclear missile submarines emerge from the Clyde.
"Without maritime patrol aircraft surveillance, opportunities for intelligence-gathering by such 'intruders' can only prejudice the security and effectiveness of our strategic deterrent.
"Indeed, it would be surprising if valuable intelligence had not already been acquired by the Russian Navy since the Nimrod force was grounded in March 2010."
The letter is signed by Air Marshall Sir John Harris, Air-Vice Marshall George Chesworth, Air-Vice Marshall David Emmerson, Air-Vice Marshall Andrew Roberts and Air Commodore Andrew Neal.
The Nimrod MRA4 was cancelled in the 2010 Strategic Defence and Security Review, as ministers attempted to fill a £38 billion black hole in the Ministry of Defence budget.
The project, designed to replace the Nimrod MR2, was already years late and hundreds of millions of pounds over budget.
Gap in UK defences
In March, the Commons Defence Committee said the lack of a maritime patrol aircraft had opened up a ''crucial gap'' in UK defences.
The committee warned that more aircraft, warships, tanks and missiles were needed to provide a convincing deterrent to further aggression by Russian president Vladimir Putin.
In recent months there have been a string of approaches to Britain by Russian planes and ships.
Two Typhoon fighter jets were launched from RAF Lossiemouth in Scotland to intercept Russian bombers heading towards the UK earlier this month.
Meanwhile, in April, Typhoons out of Lossiemouth again intercepted Bear bombers flying near UK airspace, hours after HMS Argyll was deployed to monitor a destroyer and two other ships from the country as they passed through the English Channel.