Fuel prices could increase if the Government does not step in to help save an oil refinery from closure, ministers have been warned.
Unions and an MEP said it was in the national interest to keep open the Coryton refinery in Essex, which supplies 20% of fuel to London and the South East.
The refinery has gone into administration and faces being shut down within weeks, with the loss of several hundred jobs.
Unite and the GMB said the Government should take urgent action to save the site, while Labour MEP Richard Howitt said the coalition should buy shares as part of a rescue deal.
Tony Burke, assistant general secretary of Unite, warned that the closure of Coryton could lead to fuel prices rising.
He said: "Not only will Coryton's closure rip the heart out of the community, it will also further undermine the UK's already fragile refining industry. The national economy relies on oil and the security and continuity of its supply. It is simply too important to fall victim to speculators and the whim of the market.
"The threat to Coryton once again underlines how fragmented the supply of this vital commodity is and the need for the Government to intervene and work with us to develop a strategy that brings stability to the oil industry."
Phil Whitehurst, of the GMB, said: "The UK's energy market is a complete shambles and it is high time the Government stepped in and imposed some policies. If they don't, prices will go through the roof and jobs will be lost."
Mr Howitt said: "News that the former Petroplus refinery in Germany is to be sold means that three out of five of the bankrupt company's refineries in Europe are already saved, with the French plant given millions of pounds of their government's money to stay open. Coryton is the biggest, highest quality and most efficient of the five refineries in Europe, and it is a telling indictment of our British Government that only they have failed.
"The administrators told us that an equity arrangement by Government could still be a sound basis to strike a deal with interested parties. When they do the sums they'll be forced to admit that the costs of the extra unemployment outweigh a temporary investment, which in the long run would see the Government get more than their money back."