Blair acts to rule out a total ban on smacking

The campaign to ban parents from smacking children was on the verge of collapse today.

Tony Blair is determined not to criminalise all parents who slap.

He has ordered Labour backbenchers to vote down hardline legislation outlawing all forms of physical chastisement.

But in a concession to children's rights organisations, parents could still face prosecution for smacks which bruise or mark skin.

MPs are expected to back a minor tightening of the law - leaving parents who visibly mark children with little defence in court.

The law on smacking reaches a crunch debate at Westminster today. More than 350 children's groups, supported by scores of MPs, have waged a fierce campaign for an all-out ban.

Senior Labour backbenchers who want the practice totally outlawed met the Prime Minister last night to appeal for a free vote on the issue.

But Mr Blair has ordered a three-line whip on the vote - leaving an all-out ban with no chance of success. This represents a major victory for many parents' groups, teachers and lawyers who insist the state should not interfere.

In a free vote, at least 100 Labour backbenchers would have backed an amendment to the Children's Bill stripping parents of the legal defence of "reasonable chastisement". David Hinchliffe, the Labour MP who tabled it, said "every child protection agency in the country" supports this.

Mr Hinchliffe, chairman of the Commons health select committee, added: "I also have letters from the police saying it is manageable and workable."

Today rebels were preparing to defy the party whip. Lancaster MP Hilton Dawson said: "We will have a lot of people voting with their consciences."

Mr Blair and Chief Whip Hilary Armstrong have made it clear that MPs who do so could be disciplined. They fear the Government would be accused of encouraging a "nanny state".

But Labour MPs will be allowed a free vote on an alternative amendment, tabled by Liberal Democrat peer Lord Lester, allowing "mild" smacks which do not leave any mark or bruise on the child.

Last year overwhelming public opposition forced Scottish justice minister Jim Wallace to abandon moves for an outright ban north of the border .

A spokesman for the Department for Education said that while child abuse should always be prosecuted "we do not want to see parents criminalised for setting boundaries on children's behaviour in a reasonable manner".