Peers were surprised last night by business secretary Peter Mandelson’s decision to introduce a divisive bill for part-privatisation of the Royal Mail.

That did not stop Lord Clarke, a former postman and Labour lord, shouting “shame on you” at Lord Mandelson as the bill received its first reading without debate.

Plans to sell off 30 per cent of Royal Mail to a private firm in order to raise cash to help pay for its modernisation have already split the parliamentary Labour party. Over one-third of Labour MPs have signed an early day motion expressing opposition to the government’s plans.

Among the eight additional signatures to the motion from yesterday are three parliamentary private secretaries, the rank known as the ‘first rung on the ministerial ladder’.

They are Stephen Pound, PPS to Stephen Timms, Dave Anderson, PPS to Bill Rammell, and Sharon Hodgson, PPS to Dawn Primarolo. The total number of Labour MPs who have signed the motion is now 133.

Gordon Brown’s spokesman said the government would not be seeking their resignations over the issue. Jim McGovern, the MP for Dundee West, quit his post as PPS to Pat McFadden over the Royal Mail plans when first put before Labour MPs last December.

“PPS’ are not members of the government. The government’s policy is very clear.” He added: “Lots of people sign all sorts of EDMs.”

Downing Street is now facing claims the Cabinet is also divided over the Royal Mail proposals. This was also rejected, however.

The spokesman said: “I do not accept there is any difference of opinion within Cabinet on the overall policy we are taking forward, as first announced in the Hooper review at the end of last year.”