By Clark Ainsworth BBC London Online

A charity runner wearing a mock fire-engine crosses the start line

This was the 20-mile point where a lot of runners hit "the wall" - the psychological pain barrier that everyone dreads.

As the rain eased more and more people lined the route showing their support by cheering, clapping, and whistling.

Some handed out sweets to fun runners and there were banners strewn around and bands playing loud music.

Every now again someone would spot a friend or family member running past and they would dash across the road for a quick hug.

Spectators called out names they spotted on running tops making it seem like they were supporting the runners even though they did not know them.

'Runners on their mobiles'

It helped keep up the runners' spirit - I know as I was on the other side of the barriers three years ago and was due to be running this year.

But a few week's ago I picked up a hamstring injury and that was the end of the marathon for me.

So I joined the 500,000 people along the route cheering on those running.

It gets to the stage where not only do you not want to let yourself down but you do not want to let the crowd down either.

There were loud cheers when 93-year-old Fauja Singh, who is this year's oldest runner, went past looking strong. There were people much younger than him who were moving slower.

One runner flipped a pancake as he went round the 26.2-mile course

Among the runners there were some of the usual suspects like the Rhinos, who always get a cheer, Batman and Robin, Minnie Mouse and a man dressed as a fire engine.

And for the first time I have seen people running and speaking on their mobile phones.

When competitors crossed the finish line they will have had a real sense of relief and achievement knowing they have run 26.2 miles.

For the rest of the day the capital will belong to the runners - they will be king for the day.

They can get into cabs and eat, use pub toilets without buying a drink and have free travel on the Tube for the day.

The runners are treated like royalty. The capital celebrates their achievement.

Clark Ainsworth ran the London Marathon in 2001 in four hours and eight minutes. He will run next year - barring injuries.