Danny Attfield is walking with 30 colleagues from Brentwood to the Royal London Hospital
A team of 30 Brentwood postmen are walking 20 miles from their HQ to the Royal London Hospital, where a colleague's son is fighting for his life following a motorbike accident.
The group is raising money for the Essex Air Ambulance and the Sick Children's Trust, a charity that is helping the parents of 17-year-old Jim Benton while he is in hospital.
Jim is still in a serious condition in hospital two weeks after he was involved in a serious motorbike accident in Grays.
He was riding at the time with his 16-year-old brother Joe, who is making a good recovery from the leg injuries he suffered during the crash on April 12.
Jamie, father of Jim, is expected to be walking the final part of the journey with his colleagues, who will be leaving the Brentwood sorting office in St Thomas Road at around 8am.
They are scheduled to arrive at the hospital, where they have been given permission to finish on the helipad, at around 3pm.
Brentwood postman Danny Attfield, who is organising the walk, is asking for Gazette readers' support.
He said: "I would ask that everyone gives generously for these amazing causes."