Speak to people at Barnardo's about the contract and they use words like "challenging" and "sensitive".

Barnardo’s well knows that getting into bed with the UK Border Agency is a decision that puts its reputation firmly on the line.

The charity has signed a new contract which means it will have a welfare presence inside the controversial new pre-departure accommodation at Pease Pottage in West Sussex, to be used for those families detained in advance of their “ensured departure” to their country of origin following a failed application for asylum and their refusal to leave voluntarily.

The new facility for families with children follows years of outrage over the use of Karl’s Wood, scene of serial protests about the regime there, and the closure of Dungavel in Scotland as a detention centre for families perceived to pose a risk of absconding before deportation.

Barnardo’s chief executive Anne Marie Carrie, right, says the decision to take on the new role is a “regrettable necessity”, and merely an extension of Barnardo’s long-standing commitment to the welfare of asylum-seeking families for whom it already provides help and advice in the community.

The charity points out that it has drawn a series of lines in the sand, emphasising that its now-official involvement with the deportation process will not prevent it criticising any departure from the agreed guidelines by the UKBA. If there are serious breaches, such as keeping families for more than a week, or having a revolving door there for families whose legal status becomes complicated, then it reserves the right to walk away.

“For us this is not an ideal situation,” admits a Barnardo’s spokesman, “but we felt that this was the only way to ensure a proper level of care and support to the most vulnerable children.”

The spokesman adds that the charity accepts the need for enforced repatriation only as a last resort, and that pre-departure detention should never be used for more than 72 hours.

The problem with this, as critics have not been slow to flag up, is that the UKBA’s track record on asylum seekers’ treatment is less than comforting. Over the years commitments to hold people for no more than days or weeks has stretched in some cases to months and even years. The Coalition commitment to end detention of children altogether seems to have been torn up by the very fact of Pease Pottage coming on stream.

The process of collecting families prior to detention is in itself thought to be traumatising, in particular for children.

The Scottish organisation Positive Action in Housing argues that “it is the practice of detaining innocent families, not the length of time, which is harmful to children.” It asks too how Barnardo’s can possibly counsel a child never before met in the course of a few days; a child, moreover, who will assume the charity’s representatives are responsible for their being locked up and dispatched to a country they may have never known.

Unity, which works in Scotland with asylum-seeking families, raises another concern. It points out that Pease Pottage is more likely to be used for Scottish-based families with failed cases because of the sheer distance between here and Heathrow. It also claims the furore over dawn raids in Scotland has merely led to an equally unacceptable change in tactics by security firms acting for the UK Border Agency.

Phil Jones of Unity alleges that in one recent case a family in Scotland was taken from its home at 9pm and driven south through the night, and only given access to mobile phones at 2pm the following day immediately prior to departure.

Actions like this, he says, have driven other asylum-seeking families underground. And because the UKBA has involved both schools and social services in their investigation, children have been taken out of school by families who have fled their accommodation and fear arrest.

The decision to embed Barnardo’s within the new detention centre was among the first taken by the charity’s new chief executive. Ms Carrie suggests Barnardo’s involvement will result in “a system which has ambitions to be fundamentally different, which seeks to safeguard children and treat families with compassion.”

Her problem, and that of her organisation, is that the children and families in question may well arrive via a lengthy journey in a locked private security van. In addition to which Pease Pottage is not as cuddly as it sounds: it’s run by G4S and boasts locked accommodation behind a high perimeter wall with guards on duty 24 hours. A four-year-old is unlikely to mistake this for a holiday camp.

But all of this raises a much broader and profound question for the charitable sector. If charities take the Barnardo’s route they may be accused of being accomplices to policies and practices with which they profoundly disagree.

Yet if they stay out of the system they may leave the very people they are charged to help at the mercy of officials with neither the skills nor the inclination to offer comfort and support to the vulnerable in their hour of greatest need.

Nor is this an idle question in a climate where more and more public services are sub-contracted to companies with what we might charitably call a narrow specialism. As of this month, Dungavel, which will still function as an adult immigration detention centre, will be run by GEO, a company which runs a number of prisons world wide.

It is also a company which has lost several contracts because of the conditions in its facilities and the treatment of inmates. These include the cancellation of its involvement in several penal units in a number of US States including that bastion of human rights for prisoners, the lone-star state of Texas.