The unused offices, which are awaiting updating or demolition, will provide twice as many beds as Admiralty Arch, the Grade I listed building in the Mall which was opened to the homeless last winter.
The Department of the Environment, Transport and the Regions has earmarked more than pounds 800,000 towards the cold-weather project, on top of the cost of heating and maintaining government shelters, to help some of the hundreds of homeless people over the winter.
"It is already getting very cold out there," said a department source. "We are concerned that homeless people should have a roof over their heads. That is why we are making government buildings available during the coldest spells."
The abandoned Environment Department building in Marsham Street, Westminster, condemned to be knocked down because it would be too expensive to repair, is to be opened to the homeless on 1 December.
The notoriously unpopular offices, five minutes' walk from Parliament, are to be handed over to the London homeless charity Look Ahead until the end of March.
The charity plans to provide rooms for about 40 homeless people who have been bedding down in doorways near Parliament and Victoria railway station. As well as offering three meals a day, Look Ahead will provide 24-hour supervision, medical help, counselling for drug and alcohol abuse, and advice on finding permanent accommodation.
"We are the single largest provider of cold-weather beds in London," said Anna Minges of Look Ahead. "Our target group is the street homeless. They will get meals, support and will have a nice room.
"We are very pleased that the DETR [Department of the Environment, Transport and the Regions] is doing this. It makes a huge difference."
However, the move, which is still subject to planning consents now under consideration by the local council, is likely to prove controversial.
The old Environment Department building has been compared to a stack of giant concrete shoeboxes with towers. It was vacated more than a year ago after it was decided that the 27-year-old block was beyond repair.
Until recently it has been covered in green netting to protect pedestrians from its crumbling exterior.
The first few floors of the giant complex are now being fitted with fire alarms and other safety features to prepare for the influx of the homeless. Some local residents are expected to object to the granting of planning permission to an organisation working with the homeless.
The building's towers will not be transformed into bedrooms because of the problem of meeting health and safety guidelines.
"It's a very unpopular building in a poor state of repair," said one of the block's managers.
"It is going to be demolished but it is habitable. The heating has been kept going on a standby basis and it's under 24-hour security."
The Government also plans to open the doors of St George's Court, an early 1950s Ministry of Defence building in Holborn, on the outskirts of the City. Offices once used to plan troop movements and training exercises will be converted into about 60 bedrooms.
The rooms were once decorated with walnut furniture, Wilton carpets, filing cabinets and hatstands. But MoD personnel moved out early this year to make way for builders to repair the run-down premises.
If planning consents, also now being considered, are granted, 150,000sq ft of the vacant building will be loaned to Centrepoint, the charity for the homeless which ran the shelter in Admiralty Arch last year.
The cold-weather centres are to be opened this month by Hilary Armstrong, the Housing minister, who is heading the winter-shelter scheme. Dozens of housing charities bid for use of the buildings, but the Government wanted to make sure that the supervision and daily "respite" care would be of a sufficiently high quality before it awarded the space.Reuse content