Some 27,000 police and security guards will be on duty to protect the Olympic Games in London, officials said on Monday as the operation to try to ensure next year's event passes off smoothly gets under way in earnest.

Police estimate they will have some 12,000 officers on duty for the 2012 Games while the London organising committee (LOCOG) estimates it will have between 10,000 and 15,000 private security guards.

The Games are expected to be Britain's biggest peacetime security operation and the police's National Olympic Security Coordinator Chris Allison said it would place demands on forces across the country as they dealt with cuts to their budgets.

He admitted there was concern about whether the nationwide spending reductions for police would leave the Olympic team short of certain expert officers, such as firearms units and close protection teams needed to guard dignitaries.

"At the moment we can provide them. At the moment, we are satisfied there are those skills up and down the country," he told reporters.

"I've spoken to all chief constables and asked them to consider whenever they're considering reducing specialists, can they delay any reductions until after the Games."

Last month Britain lowered its international terrorism threat level, but the Games will continue to be policed on the assumption it would be at the second highest grade "severe", meaning a militant attack was considered highly likely.

Allison said the policing operation had now begun and London's most experienced public order officer Commander Bob Broadhurst had taken up the full-time role of running it.

Ian Johnston, Director of Security and Resilience at LOCOG, said there would be thousands of closed circuit TV cameras at venues, while there would be about 400 search arches and x-ray scanners at the main Olympic stadium alone.

He said spectators would probably have to queue for about 20 minutes before getting through the airport-style security at the 34 venues although exact wait times would not be clear until nearer the Games.

"Queue times will vary from venue to venue. But we're looking in many places minutes within single digits, a norm of around 20 minutes," he said.