City Hall staff have been banned from taking short-haul flights by Ken Livingstone in an attempt to tackle carbon emissions.

The Mayor ruled that around 20,000 employees should instead take trains within the UK and to the closest European cities.

All workers at the Greater London Authority, Transport for London and London Development Agency will be bound by the new rules.

Although most never travel outside London, those who do rack up hundreds of trips each year to destinations including Brussels - where the Mayor has an office promoting London - Paris and Amsterdam.

Members of the London Assembly were also expected to vote today on a motion to stop them flying on short business trips.

Six of the top ten destinations currently flown from London's airports are short-haul journeys that could easily be made by rail. Moving these passengers onto the rail network could free up 14 per cent of the capacity at Heathrow, Gatwick, City, Luton and Stansted.

Mr Livingstone said: "Air travel produces two to three times more carbon emissions than making the same trip by rail, so it is right that we take steps to reduce flights wherever possible.

"London is connected to Europe by the high-speed rail link Eurostar meaning business travel to short haul destinations across Europe can easily be taken by train. I hope that organisations across London will use this report to swap plane for train where possible."

It is already City Hall policy that staff should not use air travel for short haul trips, unless in exceptional circumstances. However, the Mayor's confirmation of the policy now covers 20,000 staff employed by TfL and the LDA.

A report published today sets out the climate change benefits of the policy as well as its practical implications in terms of costs and travel times.

It concludes that six hours is the upper time limit for rail to be a viable business option - meaning trips to the very north of Scotland and mainland Europe may have to be taken by air.

The Mayor plans to roll the policy out to the Met Police and London Fire Brigade, however the arms-length bodies may be more difficult to sign up.

Green Assembly member Jenny Jones said: "I am pleased the GLA is getting its house in order by banning unnecessary business flights. But the biggest breakthrough will come when we get big businesses in London to adopt the same attitude to unnecessary flying."

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