THOUSANDS of fun-runners, athletes and fundraisers will show solidarity to those affected by the Boston terror attacks as they line up at the start of the London Marathon.

Amid tightened security, the competitors will observe a 30-second silence before the start of the men's elite race and mass start in Blackheath, and they have been encouraged to wear black ribbons.

Virgin London Marathon has also pledged to donate £2 for every finisher in the event to The One Fund Boston, set up to raise money for victims of the explosions.

But organisers are stressing that as well as showing defiance and spirit in the showpiece event, the participants will have fun around the famous 26.2 mile course.

Competitors include Eve Deighton, from Langley Park School for Girls, who at 18 years and three days is the youngest female runner in the marathon.

And ex-Maze Hill resident Robin Gibb, 33, who is running for the Joshua Hayday Helping Hand Trust

There will be 40 per cent more police officers on the capital's streets than last year to reassure the 36,000 runners and tens of thousands of spectators in the wake of the atrocities which killed three people and injured 180 in the US last Monday.

Events in Massachusetts reached a dramatic climax as Dzhokhar Tsarnaev was apprehended following an exchange of gunfire with police after being found hiding in a boat in a back yard in the Boston suburb of Watertown.

He was taken away on a stretcher and has been admitted to hospital in a serious condition.

His brother Tamerlan, 26, was killed on Friday in a shootout with officers.

The US authorities were facing mounting pressure as it emerged the FBI was warned in early 2011 by the Russian intelligence security service, the FSB, that Tamerlan was a follower of "radical Islam".

The FBI issued a news release which said a foreign government had said Tamerlan was a strong believer and that he had changed drastically since 2010 as he prepared to leave the US to travel to a country to join underground groups.

The FBI questioned Tamerlan but he was considered not to pose a threat.

Scotland Yard is in close contact with the FBI and Boston Police and there is nothing to suggest any resulting threat to the London Marathon following the bomb attacks.

Extra security has been in put in place around the bags of the runners, the race's baggage manager said on Sunday morning.

Phil Keith said that 34 articulated lorries would take the rucksacks of the thousands of runners from the start in Blackheath in south east London to the finish on the Mall near Buckingham Palace in the centre of the capital.

The bombs which went off in Boston are believed to have been placed in rucksacks placed on the route.

"It (security) is a problem but we have taken a lot of advice from the Metropolitan Police," he told the BBC.

"We have increased the security around the baggage.

"It is all very safe. Everyone will be incredibly safe at the finish and at the start."