The fires broke out first, then the inmates.

The fires broke out first, then the inmates.

Early last month 26 men escaped from an immigration detention centre called Campsfield House in Oxfordshire. All were foreigners who had finished sentences in British jails and were awaiting deportation. More than half had been caught again within a few days. One was charged with arson.

Their escape, however, sent a wave of worry through the UK's 10 immigration lock-ups.

Not least Dungavel, the Scottish baronial pile in Lanarkshire, best-known as the enforced home of the children of failed asylum seekers.

Staff, The Herald has learned, were jumpy at Dungavel on the night of the Campsfield escape. They have been for some time, sources said, since foreign ex-convicts started replacing asylum seekers as their main "customers".

One Dungavel detainee told a worker there was going to be a riot on August 5. A manager called the police. They duly turned up, kitted out in riot gear and with dogs. The Herald understands there were 30 officers present. Strathclyde Police yesterday would only confirm that it had attended an incident at Dungavel.

"There was no incident," a Dungavel insider said yesterday. "They brought all these police officers out on the word of one man. But it just shows how on edge staff are here."

The insider said workers had every right to be on edge: there are, the source said, just five people on duty at Dungavel on any night. That is guarding up to 190 people, the vast majority no longer the headline-making failed asylum-seekers or their children, but hardened ex-convicts.

"The staff don't have the savvy to deal with cons," the insider said. "The workers come from factories, from shops. It would be understandable if they were recruiting ex-servicemen or police officers. But they're not. We are not a prison. This facility was never built to hold prisoners, yet they are held here."

Dungavel was once a prison, but an open one.

Built as the summer retreat of the Dukes of Hamilton, it was also once a luxurious hunting lodge. It was Dungavel that Rudolf Hess was heading for when he was caught in 1941.

It was here too, in a room now part of the detention centre, that the former Tory prisons minister, James Alexander Douglas-Hamilton, was born.

Sources, however, insist that Dungavel, despite its high razor-wire-topped fences, is nothing like the jails from which most of its detainees have been transferred. High-security prisons, after all, don't hold children. But Dungavel does, albeit occasionally.

There were 122 children detained at Dungavel in the first 11 months of last year, up from the same period of the previous year. Youngsters don't stay long. The average detention was three and a half days in 2006, up slightly from 2005. Seven were in for more than a week, two for more than a month.

Stays are shorter and rarer, however, than three or four years ago when the Ay family from Turkey found themselves in Dungavel for a year.

Insiders, nevertheless, now worry more about the children, given who they share Dungavel with.

"It's common knowledge that there have been sex offenders here," a source said.

"The simple fact of the matter is that children should not be held in the same area as prisoners. You are asking for trouble if you put them in with foreign national prisoners. If something happens Well, it's a secure family unit, of course, but I don't think anything is secure when you are dealing with cons."

Ex-convicts held at Dungavel over the last year or so have included money-launderers, fraudsters, paedophiles, rapists and some very disturbed people with a history of violence and mental health issues, 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.

The Home Office declined to say what proportion of Dungavel's detainees are former "foreign national prisoners".

Herald sources, however, said it was rarely below 85%, a complete turnaround from when Dungavel opened as an immigration detention centre to deal with Britain's asylum crisis in 2001.

The source said: "We have got a housing estate next door. God forbid if there was a mass escape, like at Campsfield. These people are desperate. There was an escape earlier this year when a guy got out in the laundry van."

The Home Office said it assessed ex-prisoners for suitability before they were sent to a detention centre. Across the UK there are thought to be 1000 foreign criminals, all serious, being held in largely low-security immigration detention centres.

A spokeswoman declined to confirm how many staff were on duty at Dungavel at night, but said "appropriate" numbers were agreed between the Borders and Immigration Agency and the centre's operators, private security firm G4S. She added: "Families with children are accommodated in a separate building from single adults."

Steve Farrell of the Prison Services Union stressed that he believed his members were more than up to the task they were facing at Dungavel.

He said: "I think the professionalism of staff at Dungavel is second to none and the relationships between staff and detainees, in my opinion, is among the best, if not the best, I have ever seen."

The "ever-changing" character of detainees has caused some concern, Mr Farrell acknowledged. "There are certainly issues about which we have been in discussion with the company," he said.

G4S, which took over Dungavel almost exactly a year ago, was yesterday eager to cite the findings of the Chief Inspector of Prisons, who said Dungavel was the "best-run" facility of its kind and commended the centre for "examples of good and innovative practice, which could and should have been copied elsewhere."