The former sprinter’s 400 x 400 challenge over 100 miles on the South Downs Way will premiere on Run Show TV on Tuesday

Despite being short of training and running more than 400 times further than his specialist distance, Iwan Thomas conquered a 100-mile event earlier this year to raise awareness for charity.

Thomas, who has held the UK 400m record for almost 25 years, completed the gruelling Centurion Running South Downs Way 100 in England during the summer in heatwave conditions on a hilly course and in the process raised around £25,000 for Group B Strep Support, the world’s leading charity working to eradicate Group B Strep infection in babies.

“This was the most brutal thing I have ever done,” said Thomas. “The temperatures made what should have been a difficult run almost impossible for me.”

The 47-year-old chronicled the run on social media at the time but he was also followed by a documentary crew and the film is set to be shown on Run Show TV – the company behind the National Running Show – on Tuesday November 23 at 7pm (GMT).

Thomas’ son Teddy was diagnosed with Group B Strep in 2018, an infection caused by streptococcal bacteria, which can lead to meningitis, pneumonia and sepsis, and spent the first 10 days of his life in intensive care.

Thomas said: “Seeing Teddy covered in tubes and battling for his life was by far the worst experience of my life. If I can shine a light on this infection that claims the lives of so many young children then the pain of what I endured was 100% worth it.”

Motivated by this, Thomas battled injuries during the event plus horrendous blisters. He was also in danger of missing the cut-off time at certain points but was helped by fellow ultra-runner Susie Chan and he managed to finish in 29 hours and 35 minutes.

Thomas’ UK 400m record of 44.36 will celebrate its silver anniversary in July next year as he set the mark in Birmingham in 1997. Since retirement from the track he has forged a successful career on television and is a regular announcer at British Athletics events. To keep fit, he has completed a number of distance running events such as London Marathon and Great North Run.

Tuesday’s documentary has been sponsored by Nikwax and produced by UK sport and outdoor photography and videography experts PH Balance, who followed the former European and Commonwealth 400m champion around the 100-mile route.

“I am delighted to share the raw reality of what this run cost me physically and emotionally and I hope that it has helped shine a light on Strep B and the money raised can help other families like ours,” adds Thomas, who will be part of a special VIP advance premiere in London on Monday (Nov 22).