Jason Scotland-Williams, 34, was accused of jumping over a barrier midway through the world-famous race in order to achieve the impressive time, which fell just three minutes short of the world record for a half marathon.
But Mr Scotland-Williams, who is from the capital, said it was his sixth marathon and as a personal trainer he exercises seven days a week.
He told a Sunday newspaper: "I have done nothing wrong. Nobody thinks maybe I just trained hard. No one thinks 'maybe he paced himself through the first half and when the second half came he just let himself go'.
"All along the route there are stewards and people watching. There's no way you can cheat."
Mr Scotland-Williams completed the second half of the route in one hour, one minute and 42 seconds, more than three minutes faster than double Olympic running champion Mo Farah.
It took him two hours seven minutes and five seconds to run the first half, meaning his finishing time was three hours eight minutes and 47 seconds.
Virgin Money London Marathon confirmed that Mr Scotland-Williams' results were being investigated.