The children of failed asylum seekers are being held alongside hardened criminals as Scotland's Dungavel detention centre is increasingly used as a repository for dangerous foreign prisoners.

Families sent to the Lanarkshire secure complex are being forced to live alongside men convicted of anything from human trafficking to rape.

Some worried workers yesterday warned they no longer feel able to cope with the new mix of foreign detainees at the former hunting lodge after former home secretary John Reid's drive to rid Britain of ex-convicts from abroad.

A source said: "We are not a prison. This facility was never built to hold prisoners, yet they are held here. It's common knowledge that there have been sex offenders here. The simple fact of the matter is that children should not be held in the same area as prisoners."

The Home Office last night declined to say how many of Dungavel's up to 190 detainees were now ex-convicts awaiting deportation.

The source said the figure averaged around 85% and claimed staff, few of whom are from a prison background, lacked the skills or training to deal with them - or protect the children they also still care for.

Nervous staff last month called in the police on the night when 26 foreign national prisoners escaped from a similar facility in Oxfordshire.

There was no serious problem at Dungavel on the evening. But police showed up at Scotland's only detention centre for foreigners, insiders said, in full riot gear. Strathclyde Police would yesterday only confirm they had attended.

There were 122 children detained at Dungavel in the first 11 months of last year, slightly up on the year before.

Their stays tended to be short, however, and they are held in a separate unit to single adults, including ex-convicts.

Sources, however, stress that it is not difficult for detainees from different parts of Dungavel to mix, especially during the day.

Ex-convicts held at Dungavel over the last year or so have included money-launderers, fraudsters, paedophiles and rapists, sources said. Child trafficker Gilbert Deya - the preacher extradited to Kenya who had claimed to be able to make couples fertile through the power of prayer - was a Dungavel detainee.

Last night Christina McKelvie, one of the SNP's MSPs for Central Scotland, said: "Dungavel as it is currently used is not meant to be a prison and the staff are not meant to be prison officers.

"Questions have to be asked about the level of training which the staff have been given to cope with the detainees they currently find themselves guarding. Not only are those children now being kept in a place which is obviously unsuitable, they are now being kept alongside criminals who have a record of violence.

"There are some serious concerns about the detention policy being operated in Scotland as it is, but these revelations have taken those concerns to a new level. You would not, after all, put children in Barlinnie or Peterhead."

Glasgow Labour MSP Pauline McNeill, who sits on the Education Committee, said: "Asylum seekers should not be treated in the same way as ex-offenders.

"Children should not be in the same place as offenders. And staff should be trained to deal with everything from a minor offender to a serious offender and, if they are not, that is extremely alarming."

Veteran Dungavel campaigner and Green MSP Patrick Harvie last night said: "These suggestions, if true, indicate that ministers are obviously prepared to expose children and families to risks which would be utterly unacceptable elsewhere in society."

The Prison Services Union, which represents workers at Dungavel, last night confirmed it had raised issues with the company that runs the facility, G4S. But Steve Farrell, the union's Scottish organiser, said he felt staff were "second to none".

Sources last night claimed Dungavel was looking after scores of serious ex-offenders with as few as five members of staff on duty at night. Neither the Home Office nor G4S would comment on that figure. A Home Office spokeswoman said staffing was "appropriate".

The centre was given a glowing report in May by the Chief Inspector of Prisons. He said it was was one of the "best-run" facilities of its kind, as stressed by a spokesman for G4S.

The spokesman for G4S said: "The report also commented that: Dungavel was an extremely well-run establishment, founded on very good relationships between staff and detainees'."

Holyrood politicians and Scotland's Children's Commissioner, however, have previously heavily criticised the Home Office's policy of holding children at Dungavel.