A bus company's efforts to cut global warming emissions have led to services being disrupted by cold weather.
Bio fuel is being replaced by standard low-sulphur diesel
First Eastern Counties Buses, which runs services in Norfolk, Suffolk and Cambridgeshire, said bio-diesel had turned waxy in sub-zero temperatures.
The thicker consistency of the diesel meant fuel lines became blocked.
The company said it had suspended use of the bio-diesel, and was refuelling buses with ultra low-sulphur diesel which is not temperature sensitive.
Managing director Peter Iddon said the company was working with bio fuel suppliers to develop a fuel that does not freeze in temperatures below -15C.
He added: "I would like to apologise to all our customers who today experienced delays because of this cold weather.
"With the introduction of bio-fuel our intentions were to utilise a product that offered a green and environmentally-friendly alternative to diesel.
"However, our priority must be offering a safe and reliable bus service and until the problems of using bio-fuel in cold weather are overcome we must return to the use of low-sulphur diesel."