Mr Hams has lost the weight over the past year

Steve Hams, 32, said before he started training he was almost 18 stone (114kg) but had slimmed down by running and using a weight management programme.

He has run more than 700 miles in training and is hoping to finish in about four hours and 45 minutes.

Mr Hams, who is also a volunteer first aider for St John Ambulance, has already raised �1,200 for the charity.

"I have two very special reasons for running," he said.

"Firstly, I am running in memory of my grandfather who died at the beginning of December - he was an inspirational man who I know would be proud to see me complete the marathon.