If ever John Cleese fancies a new member of the Ministry of Silly Walks he could do worse than call on me after running for about 20 miles in the sun. For that is around the moment that my own personal battle to complete 26.2miles of the London Marathon turned ugly - and a little bit slapstick.

Up until this point everything had been going excellently. Mile 19 passed and I was well on track to reach the 3 hours 50 mark for which I'd trained so hard. I was having a great time - buoyed by the spectators bringing back the spirit of London 2012.

Sometimes, however, all the training in the world clearly can't prevent a marathon meltdown.

For the final seven miles, muscles I never knew existed cramped up. Why my right wrist was in spasm I still don't know.

It was hard - and to get through it I devised a method of running while counting to 100, then walking while I counted to 100.

The cheers, name calling and even name chanting of the crowd helped so much - but it was still so tough.

I texted the other half. 'Never again' was all it said.

Then mile 24 passed and I managed to run a little longer, the last mile came and went without even stopping.

Initial disappointment at a 4 hour 26 minute time soon turned into pride - at least I did it. A lifetime goal achieved.

An hour later I turned to my wife: 'I'm definitely doing it again - I've got a time to beat now'.

• David Powles was running for Ormiston Families - a regional charity supporting children and families.