I'll prove doubters wrong by repeating record UK run, says Shrewsbury-born marathon man Mark Vaz

It comes after questions were raised about his charity run, with some of the UK's top runners calling it "inconceivable".

Shrewsbury-born Window cleaner Mr Vaz has claimed to have run the 860-mile or so route in seven days, 18 hours and 45 minutes, shaving over 31 hours off the previous world record. The record-breaker has already run more marathons in a year than any other person.

But top runners from across the country have called foul on the Lands End to John O' Groats time, saying it was simply "not possible".

Gary Kiernan, an ultra runner who contributes to running website run247, said: "I have done a lot of long distance running, I know the course, I know what it takes out of you. For him it is just not possible."

Mr Kiernan penned an article in which he calls into question Mr Vaz's achievement.

Asked if the best ultra runners in the world could complete the challenge in the Penkridge man's time, he said: "No. Some of the best have come close to the world record but never beaten it. For him to do it is inconceivable."

Popular marathon runner Robert Young, who has penned the book Marathon Man and is currently in the US looking to run across the country and break a world record of his own, also raised questions.

He said: "It would have been close to beating the greatest runner ever Yiannis Kouros and that is not happening anytime soon."

Mr Vaz today said he is standing by his record and says he is in the process of sending the relevant information off to Guinness to get his world record ratified.

He said: "All I feel now is sour grapes. I do not even need to comment on the allegations, I know my time and so do my support team who were there with me.

"I am still in the process of sending all the information off to Guinness, it takes a while. I have closed my Facebook account as people are just trolling me. If people do not like what I have achieved then that is up to them."

Mr Vaz says he will be attempting to break a second world record in the summer as he aims to travel from John O'Groats to Lands End unsupported in less than 17 days.

He says he will have a Fitbit with him to track his progress and to prove his achievements.