The Government is facing a new, and potentially significant, revolt from within Labour ranks over its plans to scrap child benefit for lone parents.

More than 100 Labour MPs have signed a private letter to Chancellor Gordon Brown, urging him to put off implementing the plan.

The number of MPs backing the demand for a delay, and the fact that they represent all shades of party opinion, could force the Government to think again about pushing ahead with a plan which could see single parents lose up to #11-a-week in benefit.

The call to postpone the cut is likely to give Ministers a bigger headache than the Commons Early Day Motion earlier this week attacking the plan which attracted some 50 Labour signatories. Some later withdrew.

Critics of the cut have chosen the tactic of a private letter to Mr Brown in a bid to minimise harmful publicity and demonstrate that their opposition is constructive.

Several Scottish left-wingers, including Mrs Maria Fyfe (Glasgow Maryhill) and Mr Ian Davidson (Glasgow Pollok), have been among those collecting signatures.

Glasgow Baillieston MP Jimmy Wray, one of the 100-plus signatories, said he had signed because: ''We as a Labour Party should ensure that the broadest shoulders carry the heaviest burdens. Lone parents are the most vulnerable in society and we should never at any time be taking benefits from them''.

Back benchers who signed either wanted the Government to drop the plan altogether or wait and see if its New Deal, designed to get unemployed lone parents back into work, produces results.

One Scottish Blairite MP, who refused to sign the letter, said: ''I can understand the dismay of people who did sign it, but at the same time we've got to look at the long-term implications of our Welfare to Work programme.''