A week after his humiliating defeat in his bid for the prime ministership, Peter Dutton is facing an ever-widening row over his use of his ministerial discretion in granting visas to au pairs.

The Senate has already set up an inquiry into his decisions. Now more detailed information is emerging.

A whistleblower has leaked to Labor an email trail of correspondence showing how Dutton rejected advice from Australian Border Force, granting a visa in 2015 to French au pair Alexandra Deuwel.

Deuwel had admitted to Border Force that she planned to work on a voluntary basis, minding children and cooking, for South Australian pastoralists Callum and Skye MacLachlan. In return she would get free accommodation.

Callum MacLachlan - whose father Hugh has been a big donor to the Liberals - is related to AFL chief executive Gillon McLachlan (although their named are spelled differently).

Gillon McLachlan made representations to Dutton’s chief of staff.

An email from Callum and Skye MacLachlan said there had been a “misunderstanding” that the woman planned to work for them. “She is here to spend time with our family, as we consider her to be family.”

Deuwel had in previous years worked as an au pair for the family. Border Force told Dutton that earlier in 2015 she had been warned about breaching her visa conditions.

But Dutton granted the visa, which carried the proviso she could not do in-kind work.

Dutton told 2GB on Thursday he had made a judgement based on the case’s merit, not his knowledge of the person who had referred it. He had thought the intention to deport her was “a bit rough, there’s no criminal history, she’s agreed that she wouldn’t work while she was here.”

“I am a person of integrity. I have never been compromised. I never will. People can say lots of things about me, but they won’t say that I act inappropriately. I make decisions on the merits of these cases. That’s exactly what I’ve done and I stand by the decision,” Dutton said.

On Thursday further information emerged about one of the two au pair cases earlier referred to the Senate inquiry.

Fairfax Media reported that in this case, also in 2015, a request for Dutton to override a Border Force decision had come from a one-time Queensland police service colleague of Dutton’s. Dutton granted the woman a visa.

The Guardian reported that the Italian au pair had come to work for the family.

Opposition leader Bill Shorten said Prime Minister Scott Morrison needed to explain his view on Dutton’s actions.

“I think there are a lot of Australians who might have had someone who they wanted to stay slightly longer on a visa, but they obviously don’t have the sort of access to Mr Dutton that some people have, ” Shorten said.

Former immigration department officer Sandi Logan‏ said on Twitter:

“Tweeted a few days ago there was some "stuff” coming down the pipe. Trust me: there’s more! Niagara Falls gonna look like a trickle by the time this has run its course.“