Police yesterday raided more than 50 brothels in what is believed to be the biggest clampdown on prostitution in recent times.

Around 110 officers visited dozens of addresses in Soho, central London, this afternoon and up to 60 prostitutes - many illegal immigrants - were questioned.

Twenty-eight people were arrested in the raids, including two under the age of 16.

Scotland Yard said the raids followed eight months of intelligence gathering in a bid to stifle the vice trade in London.

Police sources said that in the brothels it would be usual to have one prostitute and a maid to ''keep the place tidy''.

Sources said officers were initially concerned that underage girls were being exploited but the investigation so far had not uncovered any such evidence.

The premises raided yesterday were mainly one and two bedroom flats, a police spokesman said. ''As far as we know, this is the biggest simultaneous crackdown on brothels and prostitution in this country in recent times.''

Chief Inspector Chris Bradford said a lot more work had to be done in London to prevent immigrant girls mainly from Eastern Europe from being exploited by ruthless pimps.