Unions have accused the Government of letting down and betraying the workers at the Coryton oil refinery in Essex after ministers decided not to apply for permission to use state funds to keep it running.
The Government would have had to get permission from the European Commission before it could subsidise the refinery. Coryton has been at risk since its parent company went into liquidation in January.
Now, it appears that several hundred employees will lose their jobs.
The Government decided that stepping in to help Coryton would not be sustainable, adding: "This would be a short-term fix, and it could potentially lead to job losses at other refineries who would be at an unfair disadvantage to Coryton."
The spokesman added that the Government is working with job agencies to find new positions for the staff and that the closure of the refinery should not have any impact on the supply of fuel to London and the South East.
However, the Unite union's Assistant General Secretary Tony Burke said, "The closure of Coryton will have a devastating impact on the local community and the wider economy, sucking out over £100 million and leading to the loss of hundreds of skilled jobs."
A GMB union official Phil Whitehurst also said: "Coryton supplies 20% of the fuel used in London and the South East of England. It is also a very important hub of employment in the Essex economy and part of our national infrastructure."
An economic impact assessment commissioned by Thurrock Council found that the closure of the refinery would cost the area millions of pounds from local suppliers and in business rates.