Hydrogen-fuelled taxis, introduced in London for the Olympic Games, are being transported on a 130-mile round trip to Swindon to refuel.
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The fleet of three low-emission cabs was introduced to ferry VIPs and officials during the Games.But the hydrogen fuelling station, at Lea Interchange near the Olympic Park, has had to close for security reasons.
The consortium HYTEC, which provided the taxis, said a new station was expected to open at Heathrow soon.
In the meantime, the taxis are loaded on a transporter to make the trip to the nearest filling station at car manufacturer Honda's plant in Swindon.
Air quality Diana Raine, co-ordinator of the HYTEC (Hydrogen Transport for European Cities) project, said: "Groundbreaking fuel cell electric taxis are running in London as part of a two year project to develop hydrogen technology.
"While arrangements for a hydrogen fuelling station at Heathrow are being completed we are using an alternative fuelling site in Swindon.
"However we expect a new fuelling station at Heathrow to be operational very soon and certainly before the end of the London Olympics."
Richard Kemp-Harper, from the government-run Technology Strategy Board, said the situation was "short term".
"The benefits for those taxis - apart from showing off some great British technology to the rest of the world - is actually that they produce water out of their tail pipes," he said.
"So the particulates and air quality - it's a big difference for London even if there's a small carbon problem with having to ship them up to Swindon to pick up hydrogen at the moment."
The fuel cell centre at Honda's South Marston plant was opened in September.
It is the UK's first commercial hydrogen filling station and is operated by industrial gases group BOC