The Met Office’s new headquarters in Exeter has been named as one of the most polluting public buildings by the Department of Communities and Local Government, which drew up a league table of the worst environmental offenders in the public sector.

The reason lies in the bowels of the building, where there is a £30million IBM machine that fills halls the size of two football pitches and is thought to be the second most powerful system in the country. Running it produces 12,000 tonnes of carbon dioxide a year. The computer is used to run weather modelling software and is also used for research into climate change.

By 2011, the computer is expected to have a peak processing speed approaching 1 petaflop, equivalent to more than 100,000 PCs and more than 30 times more powerful than what is in place at the moment. It will have 15million megabytes of memory – but will require 1.2 megawatts of electricity to run.

‘Life is full of ironies and I think this is one of those,’ said Friends of the Earth spokesman Maurice Spurway.