A new two-year pilot scheme to test the viability of gas-powered buses has been launched in London.

The capital is one of nine cities across Europe taking part in the project, which aims to reduce greenhouse gas emissions and noise pollution.

Fuel cell technology is used to power an electrical engine on the single-decker buses by converting liquid hydrogen into gas, which is dispensed into pressurised cylinders. The only by-product of the system is water, which turns into a vapour cloud as it leaves the exhaust.

Transport for London, explained that three hydrogen buses, costing £750,000 each, would run on the number 25 route between Oxford Circus and Ilford. The route from the West End to East End was chosen due to its length and varied traffic conditions.

The fuel cell buses will be subjected to rigorous ecological, technical and economic analysis, in order to compare their performance with conventional buses.

David Jamieson, the cleaner fuels minister, commented on the project: 'The government is delighted to be supporting this initiative through the New Vehicle Technology Fund programme - as one element in the UK's wide engagement in innovative clean low carbon vehicle technologies.'