The head of Britain's Olympic team has admitted that there is little organisers can do to stop lone demonstrators disrupting events at this summer's Games.
The admission came a day after an "anti-elitism" campaigner managed to disrupt the University Boat Race.
Lord Moynihan, the chairman of the British Olympic Association, warned that while security was under constant review for the Games, it took only one person to interrupt an event.
"It just takes one idiot, similar to the idiot [at the Boat Race], who causes major disruption," he said. "That's why all the security measures need to be put in place to minimise the chances of that happening. You can never completely remove it but you can do everything possible to minimise it."
Olympic officials are all too aware that protest groups will target events to make political or ideological points. There are particular concerns that events like rowing, the marathon and the torch relay – which inevitably have to take place over large distances – are difficult to secure over the entire route and will be popular targets for protesters who wish to use the Olympics to highlight their causes.
In 2008, as the Olympic torch made its way through London in the run-up to the Beijing Olympics, it was briefly wrestled out of the hands of the television presenter Konnie Huq, despite a a phalanx of muscled bodyguards sent by China to protect it. Britain's torch, which will arrive from Greece next month, is set to travel 8,000 miles over 70 days before arriving at the Olympic Stadium – a route that will be fiendishly difficult to protect.
Lord Moynihan, a former Olympic rower who also took part in the Boat Race, said the actions of the protester, Trenton Oldfield, were a "tragedy" for the rowers, who would have spent years preparing for the race.
"He obviously knew what he was doing," he told the BBC. "The two crews alongside each other only take up a small amount of the width of the river just the other side of Hammersmith Bridge, and to have got in their with a massive flood tide behind him and stay centre stream in order to have maximum effect was obviously a very unexpected result."
He added: "It is a major challenge and the Government have been aware of this since day one and work closely with Locog [the Olympic organising committee]. Every conceivable scenario is being reviewed and I'm confident no more can be done. It's not impossible but it is a major challenge."
Oxford Rower out of hospital after collapse
By Richard Hall
The Oxford rower who collapsed from exhaustion following the Boat Race this weekend has left hospital.
Alexander Woods, a student at Pembroke College, fell ill immediately after his university's dramatic defeat on the Thames on Saturday. The 27-year-old was seen struggling to breathe as he slumped in the boat. His teammates tried to revive him before medical staff arrived and he was taken to hospital.
Oxford's team coach, Sean Bowden, told BBC Radio Five Live yesterday that Mr Woods was "on his way back home".
"I think it was just a case of somebody being able to row themselves absolutely to a state of exhaustion," he said.