The Metropolitan police sought to reassure the British public on Tuesday (April 16) that the security around the London Marathon is under constant review.

The London Marathon will definitely go ahead on Sunday (April 21) police and organisers said, after explosions near the finish line of the Boston race killed at least three people and wounded more than 100.

Earlier on Tuesday police said that there has been no change to the terrorism threat to the United Kingdom.

Met Police Commissioner Sir Bernard Hogan-Howe told journalists that his force was in communication with police in Boston following the bombing of that city's Marathon on Monday (April 15).

"What we are doing is what we normally do which is take reasonable steps. So we will increase searching, we will make sure we've got more officers on the street looking after people, making sure they're kept safe but we've no reason to think they're any less safe than they were before the terrible events in Boston yesterday," said Hogan-Howe.

Preparations are underway along the course with thousands expected to line the streets.

"I think it's a very sensible thing to review our precautions. But I think first of all we'll deal with the events tomorrow, the funeral in London of Baroness Thatcher and make sure that's carried out safely and then we'll address our concerns towards the London Marathon Sunday, and in-between times we hope we'll get more information from the Americans as they try and work out what happened, who committed this crime and it may be of course there is no link at all to the United Kingdom in which case any potential threat against the Marathon is diffused," said Hogan-Howe.

The London race was first run in 1981 and has become a centrepiece of the sporting calendar in Britain where elite athletes join thousands of amateur runners who raise money for charity.

Britain's double Olympic champion Mo Farah is one of 36,000 runners set to compete in the 26 miles (41.84 kilometres) London race, which starts at Greenwich Park and winds through some of the city's iconic landmarks before finishing at the Mall.

Presented by Adam Justice