THE Royal Navy is on standby to deploy the world’s most advanced destroyer to protect the 2012 Olympics from a 9/11-style attack.

Security chiefs are drawing up plans to moor one of the navy’s new Daring class of Type 45 destroyers in the Thames estuary. The ship, which boasts a sophisticated antiair missile system, would be ready to shoot down hijacked aircraft or small passenger jets flown towards London or the Olympic site by terrorists.

Three Type 45 destroyers – Dauntless, Daring and Diamond - have been built at an estimated cost of £1 billion each. They are being fitted out and should be ready for service by 2011.

Their main armament is the Principal AntiAir Missile System, regarded as the most sophisticated of its kind. According to the navy, it is designed “to defend against supersonic, stealthy, highly manoeuvrable missiles that could use sea-skimming or steep-diving flight profiles approaching in salvos, simultaneously from several directions”.

Its 45 super-agile Aster missiles are said by its supporters to be able to track and destroy a moving target the size of a cricket ball at 19 miles.

Lord Carlile, the government’s antiterrorism expert, welcomed the involvement of the Royal Navy. “[It] is very well equipped to deal with specific threats, such as that posed by terrorists using light aircraft,” he said. “Having a frigate in the Thames is an extremely good idea.”

However, Patrick Mercer, chairman of the Commons counterterrorism committee, said such defences should already be in place. “Given our vulnerability to this kind of attack, it is very worrying that we don’t have this kind of air defence capability at the moment,” he said.

Two senior military officers said the option of deploying a Type 45 destroyer was under consideration and the proposal was expected to be approved by security chiefs.

One officer claimed a decision had been made in principle to moor HMS Dauntless in the estuary at Sheerness in Kent during the Olympics, although a second officer stressed that deployment was a matter for ministers.

It is more than three years until the Olympics and too early for any formal decision to deploy the navy to have been made. Defence and Home Office ministers would need to endorse it, as a part of “military aid to civil powers”.

The procedure is rarely invoked: one of the most famous occasions was during the 1980 Iranian embassy siege when it allowed the SAS to burst into the Kensington building and rescue hostages.

A senior Scotland Yard source, with detailed knowledge of Olympic security planning, said police had identified the need to use a warship as a fall-back should the civilian radio communications net prove inadequate as a result of a big terrorist attack.

The ship would provide a secure, independent radio net linked to a military satellite, he said.

HMS Dauntless recently conducted a successful trial in which it thwarted a simulated multiple missile attack from Typhoon fighters, a navy officer said.

There is also talk among naval officers of providing HMS Diamond for the task, as 2012 will mark the Queen’s diamond jubilee. The cost of the naval operation will be additional to the official £600m security budget for the Games, which are being overseen by Tessa Jowell, the Olympics minister.

Under present arrangements, the RAF is to be deployed if Britain comes under attack from an aircraft hijacked by terrorists.

A military official said two Tornado GR4 fighter aircraft were on permanent standby at RAF Marham near King’s Lynn in Norfolk to launch at 15 minutes’ notice. But the officer said that plan provided only limited air cover, while the new Type 45 destroyer could provide instant radar coverage of up to 250 miles.

Security chiefs say the 2012 Olympics represents one of the most likely targets for a big Al-Qaeda attack on Britain.