The Post Office said the sale of 51 per cent would enable it to keep pace with growing domestic and international competition. The remainder of the shares would stay in public hands.
The Green Paper, published last month, contained two other proposals - full privatisation and staying entirely in the public sector.
Mr Cockburn said he would welcome full privatisation, but decided to come down in favour of the 51 per cent option because it combined economic logic with the need to help it compete.
Derek Hodgson, of the Union of Communication Workers, said: 'By supporting the break-up and privatisation option, the Post Office are irresponsibly ignoring the overwhelming views of their workforce, many mail users, and the British public.'Reuse content