Excitement turned to disappointment for 47-year-old Mark Halton when he turned up to collect his London Marathon accreditation after seven months of training - to find he had been missed off the list.

Mark, a quantity surveyor from Fifield, planned to run to raise money for the dementia charities Alzheimers Research UK and the Alzheimers Society and their Dementia Revolution.

His wife Kristina said: "He had applied in September and received a reply saying 'welcome on board' and a card last week saying 'hope all goes well, good luck'. But when he went to the ExCel exhibition centre he was told there was no record of his name."

But Mark was not going to waste seven months of training.

He worked out his own route starting in Fifield and carrying on to Dedworth Road in Windsor, the Long Walk, Datchet and Holyport - the exact length of the marathon.

Kristina said: "Friends rallied round to join him at different points of the route for an hour each, as well as his daughters Laura, 14 and Kayla, 12. Kayla cycled the last couple of miles alongside him."

But he is not deterred.

He has already had phone call from the Dementia Revolution offering him a place in next year's marathon.

Nina Ziaullah, campaign manager for Dementia Revolution, explained that there had been a misunderstanding which led to the charities thinking Mark had his own ballot place in the London Marathon rather than a place as a runner with them.

She said: "We do recognise this is a heartbreaking situation, and Mark had trained hard and fundraised actively. When we discovered he did not have a place, we offered him a place in next year’s marathon. We were really pleased to hear Mark managed to complete 26.2miles anyway."

Mark already plans to keep in shape ready to take part in next year's marathon.

He is determined to raise a lot for the Dementia Revolution, a cause that has a special personal meaning for him and his family.