Hammersmith and Fulham Council has confirmed it will sell seven buildings that are being used by charities and community groups, including Palingswick House, which houses 21 third sector organisations.
At a meeting on Monday evening, councillors approved proposals to sell the buildings as part of a plan to pay off the Conservative-run authority’s £133m debt.
The council has issued a public statement saying Palingswick House is one of two locations that "may become available" for the West London Free School, which is being set up by the author and journalist Toby Young.
A spokesman for the Hammersmith and Fulham Refugee Forum, which represents 10 refugee support groups based in Palingswick House, said the council had told him all of the charities in the building would be evicted by August.
"This is an absolute disaster for us," he said. "The council has said it will provide us with an alternative place, but of the three places it has proposed, only one is anywhere near completion. One hasn’t even got planning permission yet. There won’t be enough space.
"We’ve also been told that we will have to pay full market rents for the new places. Many charities can’t afford this."
The spokesman said one of the organisation’s members, the Iranian Association, might lose its contract with the Home Office to provide citizenship tests because of the eviction. Other groups would close down or significantly reduce the scale of their work, he said.
In a statement, council leader Stephen Greenhalgh said: "We had to make a tough decision, but we would not be able to secure a strong future and protect front-line services if we didn't tackle our historic debt.
"Hundreds of council staff have relocated to save costs and we are asking voluntary sector groups to do the same. All but a few groups have risen to the big society challenge, recognising that we are continuing to provide more than £4m in voluntary sector grants - far more than other councils - and developing new community hubs, which will enable groups to share better, more accessible accommodation at a lower cost to the public purse."