The GMB union has written to the trade secretary about the potential impacts of a merger between Asda and petrol forecourt business EG Group.

The union said the proposed merger will threaten the UK's food supply, fuel prices and 100,000 jobs.

In a letter to Kemi Badenoch, secretary of state for business and trade, the union points out Asda's debts are already thought to be more than £4.7 billion and any potential merger with EG Group could add more than £7 billion to the total.

The £7 billion EG debt is due to be refinanced in 2025, when interest rates are likely to be significantly higher - placing the supermarket, which has stores in Gloucester and Cheltenham, in a perilous financial position, the union warns.

GMB has called on the business secretary to ensure the merger is fully investigated by the Competition and Markets Authority (CMA).

Nadine Houghton, GMB national officer, said: "The potential Asda and EG Group merger is likely to saddle the company with a massive, unsustainable debt burden. Allowing it to go ahead would be deeply irresponsible.

"Firstly, it risks the jobs of more than 100,000 employees. As one of the largest private sector employers in the UK, the future sustainability of the business is a matter of national, public interest.

"Secondly, it would place the future of the UK's food supply at risk, by loading even greater debt onto one of the UK's big four supermarkets.

"Finally, it will have a chilling effect on competition for fuel prices by creating a 'super retailer' of more than 700 petrol stations.

The letter concluded by saying the merger is in the best interests of neither Asda as a business nor the public and consumers.