Charity Streetlink revealed it has recorded up to 50 prostitutes working in the city's red light district.

The figure is more than double the 20 sex workers estimated at the end of Operation Kerb, the last major prostitution crackdown by Preston Police.

The revelation comes as householders claim prostitutes are starting to encroach on residential streets in the Fletcher Road area of Deepdale after being moved on from the nearby industrial estate.

Tim Keightley, director of Streetlink, which supports women seeking to quit prostitution, said: "It is likely that in a 12-month period we will contact between 40 and 50 different women. Some are from Preston, but others travel in from neighbouring towns and villages.

"But we rarely see more than eight in any given two-hour outreach session in an evening. This means impressions of crowded streets of sex workers are wildly inaccurate.

"The number may have reduced in the time of Operation Kerb, but doesn't mean they weren't turning to other methods to make ends meet.

"The operation was a temporary thing. Once it finished we always anticipated the figures would rise again. We know it will take more than that to keep women out of prostitution."

Police stressed the women do not all work at the same time and some only visit the city once.

Sgt Dave Herbert, of Fulwood Police, said there was a maximum of five or six women who regularly worked the area at any one time with others operating less regularly.

Historically, prostitution in Preston centres around industrial areas of Mary's Street.

However, the emergence of workers on nearby residential roads like Bleasdale Street East and Meadow Street, has prompted anger from locals.

Residents have now raised the issue as a priority at the area's PACT meetings.

Sgt Herbert said: "Most workers travel from out of town and aren't regulars. They come here because Preston is more built up.

"The issue is becoming a priority again because of the emergence in residential areas, which we want to stamp out.

"We are trying to keep the girls to Fletcher Road and St Mary's Street to lessen the impact on residents.

Warning letters

"In a whole year we have only had one complaint, from Bleasdale Street East. However, we are handing leaflets to girls telling them it has been raised as a priority and warning them to stay out of named areas.

"If they don't stick to that we will arrest them."

When Operation Kerb started, Preston had about 70 active street sex workers with between six and 12 seen on any one night.

When it ended five years ago there were approximately 20 active prostitutes, with two or three working at a time.

One woman, who lives in the area but did not wish to be named, said: "Some of the working girls have lived in the immediate area.

"They appear in the mornings but mostly in the evenings around 5pm when workers are leaving."

Police are encouraging residents to note registration numbers of vehicles persistently in the area so officers can send warning letters.

* The next PACT meeting for the area is at Aadams residential home on Peel Hall Street, Deepdale, at 6pm on Tuesday.

>> Take part in our survey on Preston's sex trade

>> Vote in our latest web poll