Even though I think he could do the 30 hour challenge, I believe that he cheated at London. Given the times and distances that he was supposedly running during Race Across USA, I think it is highly unlikely he would have had that type of speed in the tank for the London Marathon.
His 3:07 in London is valid. He has every 5km split, start and finish time. The course is fully lined by spectators, so there's nowhere he could have left/rejoined without being visible, and he was in his very recognisable kilt. He can be seen running from the start line in the BBC TV coverage. He can be seen at all the photo points along the route alongside other runners with his splits. There's video of him trying to keep up with the Paula train during the first 5km, and more video of him stopped talking to his support crew around 24 miles.
The 3:07 is valid and I wouldn't bet against a sub-3 with the same training but without such stupid pacing and that ridiculous kilt.