'Love rat of the year' – who became scourge of adulterers

Lib Dem MP John Hemming tells Nina Lakhani why transparency is an issue worth fighting for

John Hemming is definitely a cat man. At one time he lived with 16 of them, although today there are only two: Patch, a scratchy kitten, and Twinkle, brother of the infamous Beauty, missing since the MP's estranged wife was caught on camera stealing the creature from the house Hemming shares with his girlfriend.

Christine Hemming's conviction for burglary in September was lapped up by the media, whose interest in the Liberal Democrat backbencher has been fuelled by his parliamentary campaign to expose the use of superinjunctions: Fred Goodwin and Ryan Giggs to name just two humdingers from 2011.

The press have also been titillated by his wife's claim in court that Hemming had 26 mistresses during their marriage – something the self-nominated "love rat of the year" flatly denies as "just not true". Nevertheless, his personal life isn't without genuine intrigue. While the marriage was not an open relationship as such, for 12 years Hemming was married to Christine, with whom he has three children, aged 21, 11 and nine – while also having relations with Emily Cox, his former assistant and current bookkeeper, with whom he had a daughter, Isabel, now six, the existence of whom Christine says she learnt from the press.

Hemming, Ms Cox and Isabel now live in a spacious two-bedroom house in Moseley, Birmingham, only five minutes from his former home, where his wife and two youngest children still live. "I see bits of my kids, not lots," he says. And the relationship with his wife? "It's not particularly good."

Hemming was elected to Parliament as MP for Yardley South in 2005 at his sixth attempt, while deputy leader of Birmingham City Council.

He is awfully bothered by a lack of oversight applied to the care system – which he believes leads to miscarriages of justice in the family courts.

"Things that happen without scrutiny happen wrongly. Concealing things is not in the benefit of the children; it only benefits those who run the system who can't be held to account. I've seen the injustices. It is an unevidence-based justice system, relying on twaddle and psychobabble and they get away with it because the people it happens to are economically and politically weak."

He worries that although David Cameron's public statements about speeding up the adoption process are well intentioned, this will lead to further miscarriages of justice. "Measuring the [success of the] system by adoption means you reward councils who assess grandparents to be unsuitable. There is no getting away from that."

He adds: "People's lives are a bit murky at times, but that doesn't necessarily make them bad parents. There are situations when children cannot be left with their natural parents, but you have to have a rational system for dealing with it."

Not everyone sees him as a champion for justice. Hemming faced stinging criticism after talking of the case of the former jockey and horse trainer Vicky Haigh, who was involved in an acerbic and secret custody battle in the courts.

The Children and Family Court Advisory and Support Service (Cafcass), which advises the courts on care cases, wanted to know what Haigh had said about her case during a meeting hosted by Hemming, claiming she was in breach of a court order forbidding such discussion. Hemming insists that this constituted contempt of Parliament, as any citizen should be able to petition Parliament without threat of prosecution, and named her during a Commons debate.

"It is very wrong to try and conceal who these things happen to... I didn't go into the care proceedings. I only dealt with the very narrow issues about her right to complain."

Haigh was later publicly declared a liar and an unfit mother by the country's most senior family judge, Sir Nicholas Wall, and was recently jailed for breaching the non-molestation order forbidding her to contact her daughter. Justice Wall has personally criticised Hemming's interventions.

"This looks to me like an attempt to shut her up, basically. Regardless of what people are alleged to have done, they should have the right to an appeal, and she is being prevented of this right. And now she's in prison for three years," says the MP.

Born in Birmingham in 1960, to a supply-teacher mother and electrical-contractor father, Hemming won a scholarship to read natural sciences at Magdalen College, Oxford. By 27 he was a millionaire. His company, JHC plc, of which he remains chairman, designs internet software for financial services and has 200 employees and a turnover of £12m.

More interesting, if less lucrative, is the record company Music Mercia he set up in 1997, with seven labels featuring hard house, techno, drum and bass and punk bands. In his youth Hemming drummed for a Sex Pistols cover act.

He was the first Liberal Democrat to suggest a coalition with the Tories, helping to persuade party members. He doesn't believe a coalition with Labour could have worked and is scathing about the last government's economic policy. "Their financial strategy is complete rubbish. You couldn't agree something when the financial strategy would take the country right off the cliff. If the country goes bust, it doesn't matter what else you want to do, you can't do it."

For him, the best thing about being in the coalition is walking into the lobby with the Government, "so I can talk to ministers about things that are important".

Were the Liberal Democrats to be pulverised at the next election he says he hopes by then to have helped to change the care system. "It does more damage than good," he says, "so if I can make some progress in sorting that out that would be positive, progress in making sure the courts work properly... and if I can protect some people from oppressive and unjust actions to imprison them in secret, then that's a positive thing too. I need to achieve much more."