Campaigners trying to save jobs at Coryton oil refinery have staged a protest amid warnings that its closure could see more than £100 million drained from the economy.
More than 100 people demonstrated outside the Coryton refinery in Stanford-le-Hope, where almost 1,000 workers face losing their jobs.
Unite called on ministers to follow the example of the French government and give state aid to keep Coryton running until a buyer can be found.
Thurrock council has commissioned an economic impact assessment on the closure or change of use of the site, which found it would cost £30 million in wages, £26 million in contractor costs, £6 million in locally sourced materials, £40 million spent on chemicals and utilities, and £5 million in business rates.
Unite assistant general secretary Tony Burke said: "The economic impact and human cost of Coryton's closure will be massive. The Government cannot continue to sit on its hands and allow livelihoods to be destroyed.
"Over £100 million could be drained from the local and national economy, as well as the UK's refining capacity being undermined. Today's protest shows that the workers, who have kept the site running, feel let down and angry by the Government's failure to intervene."
Local Labour MEP Richard Howitt said: "The Government accepts that the Thames Gateway is nationally important for economic regeneration, so must not stand by while one of its most important businesses in one of the most crucial areas goes under.
"Government representatives repeatedly told us that best efforts were being made to find a new buyer, but today's protest shows that today no one believes they were telling the truth."