Gary Collings, who got on the Go Whippet! guided bus in Somersham High Street at about 7.35am, said: There were around 10 passengers on board the bus. About five minutes later we were at the first hill out of Somersham and there was a bang from the back of the bus. Then there was a hissing sound and the back of the bus swung on to the grass. We were going about 50mph at the time. We slid down the road at a 40-50 degree angle. We were just holding on to what we could and we were thinking are we going to tip over? Luckily, there were no cars coming the other way, otherwise someone would have been seriously injured. The 26-year-old, of The Trundle, Somersham, said that he and another passenger got off the bus and walked along the road to warn drivers of the obstruction. The back of the bus was stuck in the grass so the bus was blocking the road, about 15m from the brow of the hill. The fog was set in by then and the visibility was extremely low. The first thing to do was to stop other cars, so myself and another passenger went to the brow of the next hill to flag down cars as we waited for the police. It took them around 50 minutes and two calls before they arrived. He added: The visibility got so low that motorists were only noticing us as they got close by. It was dangerous and there were times when we had to get into the road to warn drivers. It was not a fun morning. A Cambridgeshire police spokesman said: We were called at 7.40am to reports of a broken down bus on Somersham Road. Officers were dispatched immediately but due to the high volume of incidents at the time of the call it took officers 30 minutes to arrive. The company had arranged for the vehicle to be recovered prior to contacting police. Peter Lee, Whippet director, was unavailable for comment.