Tricia Pritchard speaking on BBC's One O'Clock News: "There's no where for those parents to go"

Members of the Playpen campaign group told the Social Security Secretary and Minister for Women Harriet Harman that they want a national register of nannies.

The call came as the former au pair Louise Woodward returned to Britain from the United States.

Although Woodward carries a conviction for the manslaughter of a baby in her care, under British law there is nothing to stop her looking after children again.

Some agencies choose to rigorously vet nannies

Campaigners point out that child-minders, who look after children in their own homes, have to be registered and are regularly inspected.

Playpen - set up in the wake of Woodward's arrest last year - wants a national register established for nannies and au pairs.

It says a register could be used to check nannies' qualifications, exclude people with criminal convictions and protect children from abuse.

Playpen stressed it was not conducting a campaign against Woodward, who claims she was wrongly convicted.

There are thought to be 100,000 nannies and au pairs working in the UK, although the lack of registration makes any estimate uncertain.

Tricia Pritchard: "We need to know who these people are"

Tricia Pritchard, chairwoman of Playpen, told the BBC: "We really need to know who these people are, where they are and what they are doing."

She admitted there was no evidence of wide-scale abuse within the profession, but said that was partly down to the absence of a national register.

"Thankfully instances like the Louise Woodward case are very rare. But there are instances where the parents identify bad practice and there's nowhere for those parents to go," she said.

"All a parent can do is to sack a nanny. The nanny then moves on to the next unsuspecting family."

But supporters of a registration scheme know that tighter controls will push up the cost of child care, forcing some parents to go without.

Children are victims, say campaigners

"I don't believe child care should be cheap," said Ms Pritchard.

She described the meeting with Ms Harman as "extremely positive".

"We have come away quite excited. We undertook to look at quite a number of issues together, which is more than we expected. The minister also undertook to meet us again. It was very positive."