If you don't know anyone running in tomorrow's London Marathon, fret not. PC Advisor's long-suffering Online Editor, Guy Dixon, will be racing the gruelling 26.2 mile ordeal in aid of leukaemia sufferers.

London's marathon is 21 years old this year, and so far more than 445,000 runners have taken part in what is surely one of the hardest feats of endurance running any sane person would consider.

Guy isn't alone in using the marathon to raise money as well as his pulse rate. Last year three quarters of the runners in what is called the Mass Race, for all-comers, raised money for charities for every mile they clocked up, and overall they made a £24m haul.

Of course, the time to beat is that set by last year's winner Antoni Pinto from Portugal, who finished last year's race in just two hours, six minutes and 36 seconds.

For more information about the London Marathon, click here.