Downing Street has been asked to review security arrangements because insurgents apparently tried to bring down David Cameron's helicopter in Afghanistan.

An RAF Chinook transporting the Prime Minister during a visit earlier this year was forced into a last-minute diversion because of the threat.

Sources told The Times that the attempt on June 20 was "much closer than anyone said at the time", prompting calls from senior military figures for a security shake-up at Number 10.

Among the options being urged is a news blackout for future visits, to be lifted only when the Prime Minister has left the war zone, it was reported.

The threat arose during Mr Cameron's first visit to Afghanistan as Prime Minister.

He had been due to fly to the Shahzad base in Helmand to meet troops from the 1st Battalion Duke of Lancaster's Regiment.

But his Chinook helicopter was forced to change direction at the last minute to the main operating base in the provincial capital, Lashkar Gah.

Intelligence suggested insurgents might be planning to bring down a helicopter. Further information then indicated a possible attack on a VIP.

At that point the commander of Taskforce Helmand, Brigadier Richard Felton, who was due to meet Mr Cameron at the base, decided it was too dangerous for the visit to continue and it was called off.

The Times said senior military figures believe the planned attack was more advanced than previously admitted and that insurgents knew which helicopter was carrying Mr Cameron.