In a personal blog published yesterday, Andrew Purkis said there were "a number of problems" with the commission’s critique of Oxfam and, in a tweet promoting the blog, said that the regulator’s position was "contestable".
The commission launched an inquiry into Oxfam’s safeguarding last year after an article in The Times newspaper in February alleged that Oxfam staff had employed beneficiaries as sex workers in Haiti in 2011.
In its report, published in June, the commission concluded that there had been "a culture of tolerating poor behaviour" at the charity.
But Purkis, who carried out a separate independent governance review for Oxfam in late 2017 and early 2018, disputed this, arguing that there was no one single culture across Oxfam GB.
"In truth, there are many cultures, not one, and the great challenge of managing relatively decentralised and heterogeneous international organisations is to work out how best in practice to impose common policies and standard practices successfully across such a diverse universe – and at what cost," he said.
He argued that the issues stemmed from a "suspected particular cultural problem in one part of the charity’s humanitarian workforce", which he described as "a particular community of sometimes hard-bitten, hard-drinking expat white men" who were dropped into locations to deal with emergencies at short notice and who were very different from more local, settled staff.
Purkis also disagreed with the idea that even within those cultures there had be a tolerance of bad behaviour, arguing that since 2012 there had been "a growing community of staff in Oxfam GB focused on improving the charity’s record of compliance with regulatory policies and Oxfam’s own policies and rules, partly at the insistence of the trustees".
He acknowledged that sustained culture change was needed at the charity, but said: "That is not at all the same as saying that Oxfam International or Oxfam GB had a (single) culture that in general tolerated poor behaviour.
"On the contrary, more than half the battle is to build on the good practice, idealism and healthy cultures already in evidence so that they become more consistently the norm."
Purkis also rejected the idea that safeguarding should be charities’ sole priority, arguing that the "stubborn complexities" of running such an organisation meant it could only ever be one among many.
He told Third Sector he wanted the blog to "rebalance the discussion around Oxfam" and he had published the blog now because he’d wanted to wait until the dust settled in the wake of the report’s publication.
"It is right that we expect the commission in particular to be fair and careful and show some understanding of charities when it makes it public pronouncements upon them, and they need to be held to account when they fall short of that," he told Third Sector.
A Charity Commission spokeswoman said: "Our inquiry report speaks for itself. Charities and their advisers now need to ensure they learn the lessons from these events. They must recognise the importance of these issues to the public and why this matters."