Campaigners warn the crackdown will mean more women working on the streets

But it could be years before any new laws come into effect.

The Home Office has decided to respond after complaints that under the present law it is only a civil offence to put prostitutes' cards in phone boxes, making it difficult for local councils to prosecute offenders.

The consultation involved discussions with police, the Crown Prosecution Service, local authorities and phone companies.

Previously the had government asked the phone watchdog OFTEL to look at ways of barring calls to help deal with the problem.

The department has been looking at giving more powers to local authorities, but that has been rejected in favour of making it a national offence.

The necessary legislation would be introduced "when time allows".

Plan opposed

But as the Home Office already has five bills out of the 15 announced in last week's Queen's speech, so it will be after the next election - if, as expected, it is called in the spring - before any new measures can be introduced.

Labour's Karen Buck, MP for Regent's Park & North Kensington in London, introduced a backbench bill on the issue last year.

But the English Collective of Prostitutes has long defended the present advertising system, warning that to make it a criminal offence will force women onto the streets

The government's original consultation paper proposed fines of up to Ł1,000 or even jail for those caught placing prostitutes' cards in telephone boxes.

Explicit images

About 14 million cards, which often include sexually explicit images, are left in public telephone boxes each year.

In a 1997 survey it was estimated around 650 women were operating in this way in London, touting for business at the end of 400 different phone lines.

Previous attempts to clean up the problem through laws covering littering, criminal damage and indecency only led to the card distributors changing tactics.

BT introduced a policy of barring incoming calls to numbers advertised on cards but prostitutes avoided the sanction by switching to other phone companies.

Recently the cards were used by some primary school children in London - some as young as five - in a bizarre version of the Pokémon card-collecting craze.