Boris Johnson today piled pressure on the Home Secretary over the Olympics security fiasco as he admitted that “everyone” involved in the Games knew there was a problem “ages ago”.

As hundreds of extra police faced being drafted in to plug gaps in G4S’s operations, it emerged that both City Hall and the Scotland Yard had raised concerns with the Home Office over the private security firm’s ability to provide enough staff for the Games.

The Mayor said officials realised many months ago that there would have to be an “expansion” of the number of security staff at Olympic sites.

His remarks directly contradicted claims made by Home Secretary Theresa May to Parliament that she was told only last week that 3,500 troops would be needed as G4S could not deliver on its promise of supplying 10,000 guards.

The extra police from nine forces — being called up by in addition to the troops — will guard 12 venues as they are searched so they can be put in “lockdown for the Games.

G4S guards had been supposed to perform the task. A police source said: “We have a strict timetable for carrying out these searches which we cannot afford to let slip.”

G4S shares dropped by up to 10 per cent in early trading today after the company admitted it could lose up to £50million on the Olympics contract.

Nick Buckles, G4S’s chief executive, is fighting for his job over the security debacle, but it is believed he will keep his post until after the Olympics.

Mr Johnson today said Mrs May and her officials had been aware of the difficulties facing G4S for many months.

“What happened was that around about December, January, it was recognised the sheer volume of security — the need — was perhaps greater than had been anticipated,” he told Sky News.

“There’s been an expansion in the number of security personnel required — the armed services are stepping into the breach... and that’s the right thing.

“Everybody that was organising the Olympics knew this was coming up … ages ago.”

Stephen Greenhalgh, Deputy Mayor for Policing and Crime, slammed claims by G4S bosses that they had only realised the scale of the problem a week ago. He said: “It is concerning to find G4S stating that they only realised eight or nine days ago that they would fall short of the resources required.

“This issue was flagged up repeatedly by both the Metropolitan Police Authority and subsequently the Mayor’s Office for Policing And Crime for more than a year to G4S directly, the Olympic Security Board, and the Home Office.”

Mr Greenhalgh said any extra police drafted in to help with security for the Games must be paid for by G4S.

Labour’s shadow security minister Diana Johnson said: “It seems clear the only person who didn’t know that gaps in Olympic security would have to be filled by the Armed Forces was the one person who should have known. Theresa May needs to explain how and why she didn’t have a clue.”

Mrs May today said: “[G4S told us] they were not going to be able to guarantee the numbers that they were contracted to provide and in those circumstances the Government stepped in — we moved in very quickly — and announced that we would be bringing 3,500 military personnel to act as that contingency.”

She added: “It is not a shambles.”

Pressure was growing for troops to be paid a £500 bonus for securing the Games — with G4S footing the bill. Labour shadow defence secretary Jim Murphy was raising the demand in the Commons today.

He told the Standard: “Our brilliant and brave Forces should never be taken for granted. Ministers need to get their priorities straight and deliver a Forces’ Olympics bonus. G4S have caused the inconvenience and confusion and should fund the bonus themselves.”

G4S had a £7.5 billion turnover last year and made profits of £531 million. Paying a bonus to the 350,000 soldiers called up last week would cost the firm £1.7 million.

Soldiers' Wapping move

The first of a new group of soldiers who will help guard the Olympics began arriving at their temporary living headquarters in Wapping today.

By Friday around 400 troops will be living in the disused warehouse in Tobacco Dock. The MoD said that some of the extra 3,500 troops would be placed in existing London barracks such as Regent’s Park or at the make-shift camp site in Hainault.

Another venue is HMS Ocean, moored on the Thames.

G4S shambles isn’t a one-off, it’s a flaw in our defence system

At Northolt the pilots of 11 Squadron sit in the cockpits of their Typhoon fighters ready to scramble just as the Hurricane pilots did in exactly the same spot when the Battle of Britain was at its height 62 summers ago.

The Typhoon crews are match fit and ready to defend London skies for the Olympics. It is all a stark contrast to the shambolic performance of G4S, the Government’s chosen private contractor for Olympics security on the ground.

The great G4S cock-up cannot be shrugged off as just a one-off, a glitch in the system in circumstances unlikely to be repeated. It points to a fundamental flaw and shallowness of thought in the whole of government thinking about the nation’s defence and security posture and architecture.

G4S is no ordinary security contractor. It is British, one of the largest of its kind in the world, and is used extensively to support and back the Army in security, particularly in Afghanistan. If the Defence Secretary Philip Hammond has his way, there will be more G4S and their like used for the UK’s defences and security, and less Army, Navy and Air Force.

Under current government plans, the services are to be cut to 140,000 by 2015. Currently some 19,000 are stood up for Olympics security and contingency duties and 9,500 are in Afghanistan with a similar number prepared for contingencies for the Gulf crisis and garrison duties from the Falkland Islands to Ulster. In two years’ time there just won’t be the numbers available at all.

Heaven forfend that another emergency blows up where British forces will be required. However, contingency plans are already advanced for troops, planes and ships to be sent to the Gulf should things really kick off with Iran this autumn.

Under the Government defence plan shortfalls in logistics, support and security are to be made up by “contractorisation” — an ugly linguistic camouflage for more G4S. The thinning ranks are to be filled by “up to” 30,000 reserves — not unlike the recruits G4S are now having difficulty with. Besides, no one seriously thinks Britain could provide a large reserve of quality: the reserves will be ghost battalions.

Private contractors have raised serious questions since the private military company came to be seen as a cheap option for security at home and abroad some 20 years ago. Remember Sandline in Africa, and the US Blackwater in Iraq?

These outfits, however glossy their advertising brochures, are no substitute for thousands of able-bodied young men and women and services who are ready, willing and able to tackle the new and growing security tasks of the 21st century.

The G4S saga should make the Government as a whole think again.

Robert Fox