A 48-year-old father-of-two plans to run the equivalent of 35 marathons in 22 days to raise money for charity.
Bernie Hollywood, from south Wirral, hopes to finish by taking part in the London Marathon on 13 April.
Mr Hollywood is starting his journey at John o'Groats before covering an average of 50 miles per day over a 900-mile cross-country course.
He will make the entire journey with a 15ft Barnardo's billboard, weighing almost two stone, strapped to his back.
Last year Mr Hollywood became the first person to run the Flora London Marathon course seven times in seven consecutive days.
He is also one of just 50 people in the world to have trekked unsupported to the geographic North Pole.
Over the past 20 years he has raised more than £750,000 for various charities.
The aim of his latest feat is to raise £100,000 for Barnardo's which will help the charity provide counselling and fostering.