When Chris Barton dropped to his knees at mile 12 of yesterday’s London Marathon his girlfriend thought he was injured, but he was actually about to propose.

The 30-year-old had carried an engagement ring in his shorts pocket throughout the first half of his first ever marathon in a bid to pop the question when Louise Dennis was least expecting it.

Mr Barton, from Maidstone, said: “Louise has always said she wanted any proposal to be a surprise and I knew she’d never see this coming.

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“For the first few miles I was concentrating on just running but after about mile eight I started thinking about the proposal and I knew it was getting closer and closer. I was tapping my pocket every mile or so to make sure the ring was still there.

VIDEO: Chris proposes to Louise

“It was all a bit of a blur and it was really hard going down on one knee after running 12 miles, I nearly pulled a hamstring getting down there, but it was perfect, everything I wanted it to be.”

The athlete knew his partner and their families and friends would be around the 12 to 13 mile mark so he let a pal in on his secret and asked them to send a photo of the exact spot they were standing in so he wouldn’t miss his opportunity.

As it turned out, the 20-strong group made so much noise when he approached there was no way he could have missed them.

And the cheering and clapping got even louder when he produced the engagement ring and asked Miss Dennis, 28, to marry him.

Miss Dennis, who works in human resources for the NHS, said: “I didn’t have a clue. Even when he went down on one knee I thought he’d hurt his foot. It was only when he got the box out that it dawned on me.

“It was a complete shock to everyone and there were lots of happy tears. I felt bad for Chris though because we were all celebrating with champagne and he had to carry on and run the rest of the marathon.”

Mr Barton, a commercial claims adviser for an insurance company, was running for cancer charity CLIC Sargent in memory of a friend.

He finished in 4 hours, 59 minutes and 56 seconds and has so far raised £3,600.

The couple, who have been together three years and live in Marsham Street, finally got to celebrate their engagement with drinks and an Italian meal in Covent Garden after Mr Barton crossed the finish line.

Sponsor Chris Barton at www.justgiving.com/Stretch-Barton