This will severely reduce the future build-up of pension under the current final-salary scheme.
Staff who joined before 1996 will also find that their pensions will be cut more dramatically if they chose to retire early.
"We are aware that the proposed changes set out above will be difficult for those members of staff impacted," said M&S boss Sir Stuart Rose.
"But given that we expect challenging economic conditions to continue for at least the next 12 months we believe we are taking the right action to maintain the strength of our business."
Keith Bowman at the stockbrokers Hargreaves Lansdown described the figures as "highlighting challenging but not disaster conditions on the UK High Street".
But he warned that the difficulties facing M&S could not be ignored.
"Consumers globally are in retreat, the dividend payment is still under review and the group's expansion into small food outlets is now in tatters," he said.
Record day
The retailer maintained its market share in the clothing business, saying it had done particularly well in lingerie and children's clothing.
SALES BREAKDOWN
Group sales down 1.2%
UK like-for-like sales down 7.1%
UK total sales down 3.4%
Online sales up 29%
International sales up 26.9%
UK clothing sales down 6.5%
UK home sales up 1%
UK food sales down 1.1%
Figures for 13 weeks to 27 December
M&S also said 23 December had been its record day for food sales, with sales of more than £50m.
Sir Stuart noted that there had still been plenty of people coming into M&S stores, with 56 million customers in the last 10 days before Christmas.
"The volumes that we sold were greater than last year and the traffic we had in our stores was as much as last year," he told the BBC.
"We're just finding that customers individually didn't have as much to spend."
Analysts are predicting falling profits, despite the cost-cutting measures.
"The cost initiatives are to be applauded," said John Stevenson at KBC.
"With the pressure on gross margin we've got, and given the sales outlook, we still expect profits to be falling next year."
Mr Stevenson predicts that M&S profits will fall to £595m from last year's figure of £1bn.
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