The new hydrogen buses for route RV1, launched with great fanfare by Transport for London more than a month ago, have still not come into public service.
The first two hydrogen buses of a planned fleet of eight zero-emission vehicles were unveiled in early December by Deputy Mayor of London Kit Malthouse.
They were due to begin public service on the Covent Garden to Tower Gateway route from 19 December but more than a month later the new buses are yet to carry a fare-paying passenger.
TfL says that its training programme for drivers was hindered by the heavy snowfall and low temperatures in December so it decided to postpone the first public services.
"Due to the Christmas/New Year break and adverse weather it has taken longer than expected to prepare the first three buses and train all the operating staff ready for service," says a Transport for London spokesman.
"Buses have been running along the route for driver training purposes and we expect to have the first buses into service shortly."
Mayor of London Boris Johnson encountered one of these driver training exercises on his way to City Hall on Wednesday morning.
He told the London Assembly: "I have just passed a wonderful new hydrogen bus which I overtook on my bicycle – not that it was going particularly slowly – and it was looking very good.
"It's a tribute to the versatility and the kind of imagination we are showing in our investments."
The new RV1 buses are jointly funded by Transport for London, the Department of Energy and Climate Change and the European Union via the Clean Hydrogen in Cities (CHIC) project.