Defence Secretary Philip Hammond told MPs "appropriate ground to air defences" could be put in place if it was recommended by the military.
His comments came amid reports the US will send 1000 agents – including 500 from the FBI – to look after its own athletes and diplomats because of its fears over lax UK security.
The US is said to be particularly concerned about the UK’s limitations when it comes to anti-terrorism stop-and-search powers. Their worries were compounded by last week’s border control scandal.
It was revealed last week that immigration bosses at Dover, Britian’s largest port, introduced a lax regime in 2007, which allowed officials to abandon electronic checks of terror and criminal watch-lists as long as the person’s face matched the picture in their passport.
The US’s concerns prompted rumours of tensions with the US and the UK, which were snuffed out by Met chief Chris Allison, in charge of policing the Games. He said: "I feel great support from the Americans. I am satisfied the Games will be safe and secure."
The UK will mobilise about 12,000 officers at the Olympic Games, along with 15,000 private security officials, at a cost of £600 million.
Surface-to-air missiles have been available as defence cover at every Olympic Games since Atlanta in 1996 – where two people died in a terrorist bombing.
Meanwhile, it was revealed the London 2012 Olympic torch relay will pass through the set of EastEnders, carried by one of the actors in the soap, and broadcast live on the BBC.
The torch relay will travel through the show’s Albert Square on July 23, on its way to the Olympic Stadium, forming a storyline for East Enders.
In tonight’s episode, viewers will discover that the Olympic Flame will be passing through the fictional borough of Walford and that one of the characters, Billy, will carry it. It sets the scene for the live torch relay next summer.
Lord Coe, chairman of the London Organising Committee of the Olympic Games, said: ‘Today’s announcement is a great addition to the Olympic Torch relay route.
“I’m sure the people of Walford will now start planning their celebrations to welcome the flame to Albert Square. Along with people right round the UK, the residents of Albert Square will be getting involved to make this their moment to shine.”