The first person to call out my name in encouragement was a volunteer soldier and I immediately thought that he’d probably been through much worse in training, or even possibly live situations, than I ever will. That was just the start of the emotional roller coaster which is running a marathon.

For me at least. I find it best not to think about the distance ahead but tick off the miles covered. I remembered Stephen Fry on an edition of QI explaining how the Aymara tribe in the Andes perceive that the future is behind them and the past is in front, based on the reasoning that you can’t see the future but you can see the past. This is how my brain works when it's not distracted by anything other than running.

On the route through South London, I decided to “high five” as many spectators as proffered their hands and in return there were many people shouting my name in encouragement. The first time I looked for a marker I had completed 10k and was feeling great with 25% completed. Crossing Tower Bridge is the halfway point and I was still going well, but running down the Highway to the Docklands, it is dispiriting to see the better runners already on their way back into the city.  I can never stop myself applauding the runners in the opposite direction in genuine admiration. It is incredible that they are able to run so fast for so long. After 25 km I caught sight of a huge TV screen with Sir Mo Farah having finished and being interviewed. I convinced myself that to run for longer was actually a much more impressive achievement; Mo had only run for just over 2 hours whereas I would be running for 4 and a half. Surely that's much more challenging?

I had an emotional wobble after the 18 mile marker. The marker was dedicated to Stephen Lawrence and the manner of his death still blemishes our city. A boy of such great promise but his memory lives on.  I then found myself studying all the different charities people were running for, with photos of lost friends or loved ones. The realisation of how tragic and/or random life can be, together with the inescapable fact that you are completely spent and there are still 8 miles to go is a recipe for emotional turmoil. I realised I am blessed.  It’s at this stage when it’s all in the mind and the will to reach the finish line. As an architect it's fantastic to be able to run round this amazing city and the contrast in neighbourhoods and the styles of architecture and urban spaces is a welcome distraction. So that helped. At other times the kindness of complete strangers screaming “Come on Chris -you’ve got this” in genuine encouragement is just so uplifting.

My main motivation running back down the Highway was to be able to look my sponsors in the eye to say that I had run every step of the way. I had been pledged over £11,000 for the Architects Benevolent Society. By the time I next thought about the distance I had passed the 35k marker with 7 to go and, as I normally run 10k twice a week, knew I was nearly home. By now there were lots of runners not running anymore and a few being loaded onto stretchers by the increasingly busy St John’s Ambulance team. I noticed that these were mainly fit young runners, probably pushing themselves towards an overly ambitious self-imposed time target, and felt grateful that my strategy of getting round in one pace and in one piece was working. I had promised the ABS I would run the marathon but cleverly I hadn’t promised to run to beat my personal best. Just as well - I was over an hour out but then that was about 20 years ago.  I sprinted (in my mind but sadly not witnessed in the photos) over the finish line.

I pocketed my medal and walked to the office for a shower. I then found somewhere to watch Manchester United going through the motions of putting in some small resemblance of the effort of each and every one of all my marathon heroes and life resumed as normal. But for 4 hours 40 minutes it was an emotional whirlwind, which really helps to put lots of things in perspective and gives me a sense of gratitude which will last a very long time.