When the youth charity Catch22 was a partner in a successful £450m bid by the giant services company Serco in 2010 to build and run a prison in south-east London, it was criticised by parts of the voluntary sector.
The Howard League for Penal Reform and the community infrastructure body Navca even asked the Charity Commission to rule that running a prison was not a charitable activity - something the commission declined to do.
Since then the new prison, Thameside, has begun operating, Catch22 has signed a deal with Serco to work in another private sector-run prison in Doncaster and the Howard League chief executive Frances Crook has renewed her criticism in an article for thirdsector.co.uk.
But Chris Wright, chief executive of Catch22 since Joyce Moseley left last year, is adamant that it was right to sign agreements with Serco and says the objections of opponents do not hold water. "Anyone who thinks charities shouldn't be running prisons is less than informed," he says. "I would like to understand their arguments."
Wright, a former probation officer, says he thinks too many people are jailed: "But the reality is that if they are locked up, it's incumbent upon me to do whatever ensures they don't get locked up again. We want to deliver services to those in need - in our opinion, the best partner for us to do that is Serco."
Wright says the role of Catch22 in the prisons where it operates with Serco is to do what many charities have done in penal institutions for many years - help prisoners reintegrate into normal life and prevent them reoffending.
But being part of the bid and having its name on the contract has, he says, given it more opportunity to ensure its services are not just an afterthought. It had the chance to design the service, and have it accepted by the main contractor, before the contract started.
The charity has some influence on the day-to-day running of the prison, he says, but this is focused on - and limited to - ensuring the right conditions to minimise reoffending. "We work on offender management, - sentence planning, case work and resettlement," he says. "We're responsible for their prison care.
"Our principle is one assessment, one case worker, one relationship - and we've had a crucial impact on the way Serco delivers these services."
Wright says he is aware of the reputational risk in running prisons and working closely with large private sector contractors, and he is aware of allegations that Catch22 was used as "bid candy".
But he says this counts for less than what is best for his beneficiaries, and that this charity is an important partner.
"Of course we aren't equal partners," he says, "but we're treated with respect and regard. When we bid, we bid as a partnership, and we contribute to operational solutions. The work we're delivering is designed by us and funded by Serco."
The contract, he says, involves a payment-by-results element based on levels of reoffending, but the charity has not had to bear that risk. "For Serco, 10 per cent of the contract is at risk," he says. "But Serco is paying us."
He says that his organisation has gone into the relationship with its eyes open. "We aren't naive," he says. "This isn't a big, bullying private company lording it over a little charity. Our relationship with Serco isn't one that just happened. We've worked with it on prisons since 2006, after a period of due diligence. We took an informed view we could form a good relationship."
At the moment, he says, charities that want to be involved in the biggest government contracts have little option but to partner with larger organisations - and that usually means the private sector. "We're a £50m organisation," he says. "We can win contracts worth £10m. If we want to go above that, we need to partner with a bigger organisation."
But he is keen to see the emergence of social sector organisations that can challenge the big private providers. "I'm very interested in the emerging social enterprise sector and whether it can provide an effective opposition to these organisations," he says. "If the emergence of social enterprise drives better quality services, that's a good thing."
In the meantime, he says, the sector must learn to stand up for itself in contract negotiations: "No one forces these arrangements to take place. In my experience, many private sector players are interested in how they might work better, and see the sector as a way to get to people that they can't reach."
In the end, Wright says, prime contractors want to benefit the sector. "It's not in the interests of Serco and others to get a bad press," he says. "And if you're in a partnership, you want your partners to be happy. You don't get that by treating them badly."
2011: Chief executive, Catch22
2008: Chief operating officer, Catch22
2006: Director of services, Rainer
2001: Head of performance, the Youth Justice Board for England and Wales.