Runner's slow route to last place.
Greg Billingham, 39, from Stockport, a first-time marathon competitor, arrived at the finish line at noon.
He hopes to have reached his target of raising pounds 30-pounds 40,000 for charity Children with Leukaemia, which is dedicated exclusively to fighting Britain's biggest childhood cancer, surrounded by well-wishers putting coins into boxes strapped to his waist.
He hatched the plan to "run" at a snail's pace, averaging three miles every 10 hours, because people who become ill find their lives have slowed down.
The technique he developed involved lifting each leg in the air for several seconds.
He made up his own training regime, which involved moving very slowly on a treadmill, slow-motion swimming, and running slowly in a farmer's field "where nobody could see me".
He confessed he had not planned his amazing feat meticulously.
"When I turned up in London, I had a tenner and a sleeping bag," the building developer said.
He found the initial leg of his journey difficult, and received some strange looks.
"It was fantastic, the people have been brilliant," he said.