Britain will mobilize the largest security operation in its peace time history for the .London Olympics.

Earlier April, hundreds of firms were told to step up warehouse security to stop potential terrorists from planting bombs in lorries that could enter the Olympic Park.

Meanwhile, the Metropolitan Police has said that 52 officers will protect the 70-day Olympic torch relay starting on May 19.

"Sadly, we have had to deal with threats of international terrorism for many, many years," said Chris Allison, national Olympic security coordinator from the Metropolitan Police.

"Our planning assumption is that the threat from terrorism will be severe," Allison said.

The 7/7 bombings in London, which killed 52 people on July 7, 2005 the day after London won the right to host the Olympics prompted massive security planning by Allison's team.

The Metropolitan Police held a series of live tests, the last of which finished this month and involved more than 4,000 individuals, to ensure cooperation between the various emergency services in London works seamlessly during the Olympics.

"So what we've ensured is that for all the venues, for all the live sites, we're putting in place the appropriate security measures," Allison said.

The riots in London last summer also raised visitors' concerns about the city's street policing, after images of burning buildings and looted shops were shown globally.

About 15,000 people took part in England's worst disturbances for decades, which began in inner London when a protest against the fatal police shooting of a suspect turned violent.

Some of the violence took place just a few kilometers from the Olympic Park, in boroughs such as Hackney. Five people died in the unrest.

Allison said large command structures had been put in place to ensure that last summer's riots did not happen again.

"What we saw last summer was something that was completely unprecedented," he said, adding that unrest of such a scale has never happened in the 28 years of his police career.

"What we'll have in London is a significant policing operation, which we didn't have last summer because we didn't anticipate what occurred then," he said.

The British government has earmarked 600m pounds ($977m) for security, but part of the 2 billion pound contingency built into the 9.3 billion-pound Olympics budget can be drawn on if needed.

The Metropolitan Police said it will draw on forces nationwide to deliver the required 12,000 officers on peak days during the Games 9,000 of which will be deployed in London.

Allison emphasized that policing does not only focus on Olympic venues, but also other busy places around the country, such as railway stations and shopping centers.

"The Olympics is not just about London. We had to ensure that we have the right officers from across the country mobilized, and we've been working to ensure that wherever you go, the policing operation looks the same," he said.

Allison's words were echoed by Britain's Prime Minister, David Cameron, at a recent press conference.

"There will be more police on the streets, there will be boats in the Thames, helicopters in the sky, troops will be assisting us to secure the venues, and intelligent services will be working around the clock," Cameron said.

The exposed venues, notably the road cycling route which takes in 93 miles of roads around London and Surrey, will have additional security measures beyond barricades lining the route.

Thousands of trained stewards, as well as some of the 70,000 volunteers, will be responsible for watching the crowds for unusual behavior.

The stewards will stand about 25m apart on the edges of the race courses for the marathons, road cycling races, road walks, open water swimming and triathlon races.

"Our focus is to make sure that 10.8 million spectators who are coming to the Games come and have a fantastic time, and are safe and secure while they are here," Allison said.

contact the writer at cecily.liu@chinadaily.com.cn