A spokeswoman, Jane Cowmeadow, said the marathon always took the safety of its runners extremely seriously and worked closely with police. "We will keep everything under review," she said.
In what will prove a major security headache to police and anti-terrorist officers, about 27,000 people are expected to run the 26 mile course through the capital on Sunday. Hundreds of thousands more usually turn out to cheer on participants in one of London's most popular sporting occasions.
But the two bomb warnings less than an hour before Saturday's Grand National was due to take place show the chaos that can be caused to such events.
No explosives were found, but police and security officials could take no chances after the bombs which detonated at Wilmslow railway station in Cheshire and the further devices which brought havoc to the motorway system last week.
Security was also tightened for yesterday's Coca-Cola cup final at Wembley stadium between Middlesbrough and Leicester City.
Specialist police teams scoured the stadium conducting fingertip searches until minutes before fans were allowed in at 1pm, two hours before kick- off.
Many fans heeded police pleas to arrive early and to save themselves trouble in case of an alert by leaving their cars on the outskirts of the city and making the final part of the journey by public transport.
Alan Gale, of City and Suburban Parking, which runs the parking for Wembley, said traffic was relatively light.
"The bulk have come by public transport and the others seem to have come in coaches. What the reason for that is I couldn't say, but we certainly have less cars than normal."
At Wembley, Middlesbrough fan Geoff Parry said he thought the security at the stadium was very good. But he added that he did not understand why terrorists would target big public events.
"I think they're going down the wrong route by targeting the people and they'll never get any sympathy by doing it," he said.Reuse content