I recall using an AEC steer to pull a 32-tonne liquid nitrogen tanker half-loaded from Slough gasworks to Hitchin gas works via Rickmansworth where a steep hill had been wet. The half-load rolled back over the trailer axles and left me with no traction so I was stuck on the hill until the cops turned up to help me reverse back down the hill. They then led me around some lanes and past the Watford Scammell works in order to bypass the hill.