Britain needs to invest now to build up VIP protection squads, specialist firearms teams, dogs and mounted police to guard the 2012 Olympics, the security chief for the London Games said on Tuesday.

Scotland Yard Assistant Commissioner Tarique Ghaffur said police wanted to operate with a "lighter touch", telling a London conference: "We have to safeguard the Games without affecting the Olympic look and feel."

But he said there was a need for "serious capability building" in what he called protective services, such as guarding visiting heads of state and controlling crowds with mounted police.

"I think the key requirement for the Olympics in terms of building capability, in terms of investment, essentially is in the area of protective services," Ghaffur said in a speech to the Royal United Services Institute.

Many forces around the country had scaled back their dog and mounted police teams, he said, and training for such specialised roles takes two to three years.

"We have to invest early," Ghaffur said.

David Evans, 2012 project director for the British Security Industry Association, said the Games were facing a big shortfall of private security staff, particularly for screening an estimated 10 million spectators passing through metal detector gates and having their bags checked.

He said the government's Olympic bid had assumed some 6,500 staff would be needed for this, and would come from the private sector.

But the industry estimated the number required at more than 7,800 people at the height of the Games and could only supply a fraction of that. "I think we're going to be about 6,000 people short at Games time," he said.

Evans said students could be recruited to carry out such security checks at the venues. "At that age, why shouldn't they? We've got 18-year-old soldiers out in Afghanistan. You can teach people how to do that properly and they'd be enthusiastic too," he told Reuters.

Some 600 million pounds is currently budgeted for security at the 2012 Games, but Conservative sports spokesman Hugh Robertson said experience from Sydney 2000 and Athens 2004 showed the risk of overshoots.

"Security costs have been the single largest driver of cost over-runs in previous Olympics," he said. The overall budget for 2012 now stands at 9.3 billion pounds.

Ghaffur told reporters: "We have a planning guideline, which is 600 million, that's what we're planning to. If there is any additional (need), we'll go to ministers."

He said police would need to bring in 1,000 to 1,500 officers from outside the capital to reinforce security at peak times. Some retired officers would also be recalled, and volunteer police would be boosted: the special constabulary in London would increase to 5,000 from 2,000 now.

Ghaffur declined to talk about the controversy over alleged racism against him in the Metropolitan Police. "I'm not going to comment on that, I'm continuing to do the job. I'm focused on my job," he said.