The UK will be left “woefully underprepared” for any potential conflict if steel blast furnaces are allowed to close, the Government is being warned.

The GMB has written to Defence Secretary Grant Shapps saying that losing the ability to make steel from scratch will “significantly impact” the security of the country’s essential defence supply chains.

The warning follows news that blast furnaces at the country’s biggest steel plant, Port Talbot in South Wales, are to close with the loss of up to 2,800 jobs in a move to a more greener way of producing steel.

Tata is planning to replace the blast furnaces with an electric arc furnace, which can produce recycled steel.

The GMB said there are fears that British Steel plans to close its blast furnaces at Scunthorpe, leaving the UK with no way to make “virgin” steel.

Matt Roberts, GMB national officer, said: “We live in a turbulent global environment.

“Both Nato’s defence chief and Mr Shapps himself have warned that war in the next two decades is a possibility.

“Yet we are on the brink of losing our full ability to make our own steel, vital to our defence industry, not least in building warships.

“It’s utter folly.

“GMB is very clear, we must retain sovereign capability to make virgin steel.”

Tata bosses are due to appear before MPs next week to answer questions about the Indian multinational company’s decision to shut down the Port Talbot blast furnaces.

On Wednesday, Tata Steel’s chief executive Rajesh Nair and Thachat Viswanath Narendran, the global chief executive and managing director, are scheduled to give evidence to the Welsh Affairs Select Committee.