Workers at carmaker BMW's Mini plant in Oxford have been told they need to pay more towards their pensions.

Managers say people living longer, falling interest rates and rising inflation mean the cost of the scheme is soaring, while employee contributions have stayed the same.

Now they want staff to consider options, including increasing contributions and cutting early retirement provisions.

Unions have reacted angrily to the proposals. In a letter to members, Dave Osborne, national secretary of the Unite union, said: "BMW has tabled proposals which in effect amount to a draconian attack on your pension scheme and your entitlements in retirement.

"The proposals are wholly unjustified, particularly when BMW, one of the most profitable car companies in the world, returned profits of £3.2bn in 2007."

Plant union convenor Bernard Moss added: "This scheme is one of the top 25 pensions in the country and we want to keep it that way."

BMW said it had ploughed in £150m to cover a deficit in the pension scheme since 2003 and was committed to adding a further £23.6m every year to remove the deficit by 2017.

Spokesman Rebecca Baxter said discussions were still at an early stage. Any changes would not affect current pensioners.