POLICE believe indoor prostitution in Strathclyde alone is now worth at least £60 million a year.

Detectives identified almost 900 active "profiles" of women advertising online across the west of Scotland in their biggest analysis yet of off-street vice.

Their interest comes as officers enjoy greater success than ever before in detecting brothels, finding 14 in 2011-12.

The figures on the scale of the vice trade in Strathclyde were compiled by a team led by Detective Inspector Clare McGuckien.

She said: "These figures are conservative. We only have statistics on the reported world, about reported crimes we have involvement in."

Glasgow prostitution has gradually shifted off-street recently despite a zero tolerance stance on brothels by the council, police and other agencies.

Ms McGuckien's team identified a total of 2067 profiles for indoor prostitutes, of whom 898 were described as active.

An average prostitute works 60 hours a month for about £100 an hour, earning themselves – and more likely their controllers – an average of £6000 a month.

However, Glasgow's outdoor vice trade has not disappeared. Agencies work with women in street prostitution, most of whom have addiction problems.

Glasgow Community Safety Services (GCSS) engages with around 450 women associated with street prostitution, though that does not mean they are all working at any one time.

Louise Belton of GCSS Glasgow believes a new middle market is emerging between the street prostitution of old and the brothel-based business.

She said: "There are almost three tiers of prostitution.

"The ones who are involved in 'on-street' have significant addiction problems, are heavily involved in the criminal justice system and are not run by pimps as such, although they are often encouraged by other girls or a boyfriend feeding a habit.

"There is a slight move off-street for some women who still have addictions.

"They are not the stereotypical brothel glamour girls. These are girls who, for whatever reason, are trying to get away from the police and they are in a flat.

"But they have more of the characteristics of somebody involved in street prostitution."

Law enforcement sources now talk of women from the streets trying indoor prostitution.

There are also concerns about trafficking of women to work in brothels. A first conviction was achieved last year against a Scots gang. Strathclyde has also had success against Chinese organised crime groups running Thai prostitution rings in Glasgow.

Women working in the street are routinely charged. So are men with the number caught kerbcrawling in Glasgow up 80% in 2011-12 to the highest figure since legislation was introduced.

However, a woman working on her own in a flat can escape prosecution, and a man visiting is committing no offence. Several MSPs hope to change this.