LONDON: Britain has written to Europe's competition chief challenging plans by auto parts maker Magna to buy carmaker Opel, as fears of job losses gather steam, a report said Thursday.

Business Secretary Peter Mandelson said the Canadian company's plans for restructuring of Opel were too expensive and susceptible to "political intervention", the Financial Times said.

"We do not believe the case has been demonstrated that the current Magna proposal is commercially the most viable plan," Mandelson said in the letter, obtained by the newspaper.

"Capacity at highly efficient plants in Britain and Spain is planned to be under-utilised, in favour of higher utilisation of some of GM?s other less efficient plants," he said.

The letter sent Tuesday to European Commissioner for Competition Neelie Kroes comes as fears mount of thousands of job losses across Europe, and possible plant closures as part of Magna's plans for Opel.

Britain has 4,700 workers at two plants at Opel's Vauxhall operations.

Mandelson urged the European Commission to take up the case "to ensure a commercially-based outcome rather than one determined by political intervention and subsidies."

Earlier this month, struggling US giant General Motors announced the sale of a majority stake in its European arm Opel to Magna and its partner, Russian state-owned lender Sberbank.

Magna was the candidate favoured by German Chancellor Angela Merkel, who faces national elections this weekend, on the grounds it would limit job losses in Germany.

Belgium, Spain and Britain have all raised concerns that the Opel sale to Magna would see them at a disadvantage compared to Germany which has backed the deal with 4.5 billion euros (6.6 billion dollars) in state aid.

Commission officials told the FT that they would "carefully examine" aid for Opel linked to its restructuring from Germany or any other member states.

According to a business plan leaked to German media on Tuesday, Magna is poised to slash around 11,000 jobs out of about 45,000 in Europe.

Thousands of car workers and supporters, including hundreds from Germany, protested at a threatened Opel factory in northern Belgium on Wednesday.