It is thought the van stopped on the M69 slip road near the M1 junction because the prisoner appeared to be harming himself.
Chief Inspector Chris Rollings of Leicestershire police said the exact circumstances were not yet known, but the prisoner, who has not been named, took the "opportunity to escape".
Mr Rollings said the escaper - described as white, 5ft 10in, with light coloured hair, who was wearing black jeans and a navy sweat shirt - was not carrying any money. He urged the public not to approach the prisoner, who was on remand for aggravated burglary.
Group 4 said the prisoner was "extremely violent in the struggle with two guards, overpowering both the men before escaping".Reuse content