They added: "The Official Receiver's first priority remains ensuring the safety of the refinery and its workers [and] he is working closely with the company's management and the Health and Safety Executive and is confident in the measures which are in place."

Negotiations were also taking place with a number of parties to progress bids with the objective of achieving a sale of the business, the spokesperson added.

It comes after Unite's general secretary Sharon Graham wrote to Energy Security Ed Miliband to share the union's concerns.

In the letter, she said: "Workers on site have informed union representatives they are keeping their options open and are not planning to work their notice period, but simply leave at the end of a pay period.

"Unite believes the financial package to retain staff during the winddown is insufficient to ensure the minimum safe staffing levels, particularly if it looks like the refinery does not have a future," Ms Graham said.

She also said it was "essential" for the workers who remained to have experience and the appropriate qualifications.

"We do not believe this is currently the case," she added.

Ms Graham's letter likened the consequences of a major incident at the North Lincolnshire refinery to the BP Texas City refinery explosion in 2005 and the Pembroke refinery explosion in the UK in 2011.

Both incidents saw multiple fatalities.

"The lives that could be lost, livelihoods destroyed, the environmental and infrastructure damage that could be done to the site and everything around it is frightening," Ms Graham wrote.

Ms Graham said union representatives were due to meet with the energy secretary next week.

Those impacted by redundancies are due to be informed by no later than the end of September, according to the Local Democracy Reporting Service.

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