A lot of people might shudder at the thought of running 26 miles during a heatwave but one determined man wasn’t going to let passing out stop him from completing a marathon.

Drew Heatley of Leyton collapsed due to heat exhaustion while competing in this year’s London Marathon to raise cash for Worldwide Cancer Research.

Three months on, the 31-year-old is speaking out about the driving force behind his will to finish the race – his late mum Christine whom he lost to cancer in 2012.

And the runner who raised more than £4,000 for the charity is keen to encourage others to donate to help find a cure for cancer.

This year’s event, held on April 22, was the hottest on record, with runners competing in temperatures reaching 23.2C.

“If Mum was here she would find it amazing that I’ve achieved it,” said Mr Heatley.

After being diagnosed with cervical cancer in 2009, Mrs Heatley received chemotherapy and beat it before it returned in 2011, spreading to her bones.

Mr Heatley started running after his mother’s diagnosis, as a form of therapy, and after her death he decided to use his fitness to benefit others.

“I felt I had to contribute in some way to help save future lives and what struck me about Worldwide Cancer Research was the science aspect,” he said.

“These amazing scientists all over the world need to be able to make progress and find new cures and treatments and they can only do that with funding through the charity. I felt I had to do my bit.”

But with just one mile to go, Mr Heatley thought all his efforts were about to be wasted when his legs gave way.

“I had completely overheated and had a body temperature of 39 degrees,” he said. “I really thought I’d blown it.”

Thanks to help from a medical team and his wife Emily, he eventually made it across the finishing line after a gruelling five hours and 13 minutes, which, he believes, would make his mum “burst with pride”.

He added: “I wasn’t sure I could get back up again but I thought of mum and all the people who had sponsored me and I knew I had to finish. I needed that medal so I walked the last 600 metres.”

Although Mr Heatley admits it was a tough day for him, he hasn’t let the ordeal put him off running and hopes to complete another marathon next year – but this time in autumn or winter.