The buyback was a part of the M&S defence against Philip Green

Investors will get between 332 and 380p per share - below the 400p Philip Green offered them in the summer when he tried to buy the ailing retailer.

The buyback is a key part of the restructuring plan announced at the time of the takeover bid by the owner of Bhs.

M&S insisted it was correct to reject Mr Green's offer despite the fact that its shares currently trade below 400p.

"Our rejection of Mr Green's potential offer was not a promise to return the share price to 400p in a matter of months," M&S chairman Paul Myers told investors at an extraordinary general meeting.

"The rejection was about the value of your investment over the longer term, as our plan begins to bear fruit."

M&S will announce the exact price of the shares next week, with payments to investors taking up the offer due soon after

Of the shareholders who voted for the buyback plan, 99.54% were in favour.

The approval follows an M&S trading statement on 12 October, which said sales fell by 5.5% overall in the second quarter compared to the same period last year.