FIGHTER jets thunder above the English countryside. Missiles stand ready. And Big Brother is watching like never before.

The London Olympics are no ordinary games. Not since the Second World War have Britain and the US teamed up for such a massive security operation on British soil.

Hundreds of American intelligence, security and law enforcement officials are flying across the Atlantic for the games that begin on July 27. Some will even be embedded with their British counterparts, sharing critical intelligence and troubleshooting potential risks. Dozens of Interpol officers will also be deployed.

The unique collaboration is rooted in common threats the partners have faced since the September 11 terror attacks on the US and Britain's own deadly suicide bombings in 2005.

Britain was America's closest ally in Afghanistan and Iraq, making it a prime target of Islamic terror groups. And dozens of recent terror plots, including the 2006 plot to blow up nearly a dozen transatlantic airliners, have been hatched within Britain's sizable Muslim population, more than a million of whom have ties to Pakistan.

Although other Olympic Games have taken place since September 11 2001, London poses a different breed of security challenge. "I'm confident that there is more than adequate security here for these games," Louis Susman, the US ambassador to the UK, said. "That said, we live in a tumultuous world, whether that be in New York or London."

Intelligence officials say there has been an expected increase in chatter among extremist groups, but there are still no specific or credible threats to the London Games. The terror level is labelled substantial, a notch below severe, and what it has been for much of the past decade. A substantial threat level indicates that an attack is a strong possibility.

"There is a perception in some quarters that the terrorist threat to this country has evaporated," said Jonathan Evans, head of MI5, Britain's domestic spy agency. "Bin Laden is dead, al-Qaeda's senior leadership in Pakistan is under serious pressure, and there hasn't been a major terror attack here for seven years.

"(But) in back rooms and in cars and on the streets of this country, there is no shortage of individuals talking about wanting to mount terrorist attacks here."

The potential threats to the London Games are broad and diverse and include the sort of lone-wolf attack like that launched by Norway's Anders Behring Breivik, who has confessed to killing 77 people.

Although al-Qaeda has been weakened by targeted US strikes, its affiliates in places like Somalia and Yemen have stepped up their activity and increased their capabilities. They have even been working on bombs that can pass undetected in airport scans.

British security officials fear that dozens of nationals who went to train in Somalia and elsewhere could return. "Terrorist problems have a long tail," said Mr Evans. "They very rarely just stop."

Up to a million visitors are expected for the games, putting added strain on border security agents at airports like London's Heathrow, which has been criticised for its long lines and lack of staff to screen those arriving from other countries.

On site, about 300000 people are expected to flow into Olympic Park in east London each day during peak times.

One of the key functions for Interpol, the international police organisation, will be to speed intelligence data-sharing between countries so that threats can be deterred. UK officials scan Interpol data 130-million times a year, Interpol secretary-general Ronald Noble said. "The truth is, and we know this from Norway, that you can't identify one ethnic group and say that's the ethnic group that should only concern us," Mr Noble said. "But this Olympics, from all that I know and based on all the information that Interpol has, should be a safe Olympics."

Shared intelligence, better technology and boosted resources have allowed security officials to crack organised plots before they happen, but the possibility of a self-starter extremist who operates below the radar remains one of the biggest fears.

Sapa-AP