With Botany MP Pansy Wong resigning from Parliament last week, Labour's chief dirt-digger and mudslinger Pete Hodgson claimed his second ministerial scalp.

But the biggest prize - John Key - has eluded him so far and Mr Hodgson believes the prospect of nailing the Prime Minister is getting dimmer.

Mr Hodgson retires at the next election after 21 years as an MP, and when he rises to speak during Parliament's question time, it's often clear that day can't come soon enough for some. Mr Hodgson's questions about Government MPs' and ministers' probity are invariably met with a barrage of abuse - more often than not the words "gutter" and "sewer" and "rat" are clearly discernible.

"That doesn't hurt me," he told the Herald. That abuse is largely restricted to the debating chamber and he is friends with some National MPs outside the House.

"I suppose there will be quite a few National MPs who will avoid talking to me. I don't really notice that. No one comes up to me personally and says derogatory things, which is just as well because I would say the following things: 'Please understand the nature of Opposition', and, more pointedly, 'If people stayed within the rules there wouldn't be any problems, would there?"'

He is not, he says, "motivated as some sort of self-appointed policeman".

"I simply think that this Government is much slacker than the previous one and much slacker than the Government before that.

"There's a certain cavalier approach in my view and it occurs from the top."

But when in Government, Mr Hodgson's own party was hardly faultless, with the names Taito Phillip Field and David Benson-Pope springing to mind.

In fact, bitter experience has shown Mr Hodgson the political gold to be extracted from digging for dirt.

He perks up at the prospect the shadow immigration portfolio he now holds might yield a scandal. "It would be rather good if it did. That would damage the Government in the same way it damaged us.

"Of course there's a political component" to his work, he says, but that comes "roughly" second to calling the Government to account.

Mr Hodgson says he fell into the role "by accident" when media reported the then Internal Affairs Minister Richard Worth - his first ministerial scalp - went to India "to do things that he might not have been wise to do and I started looking into it".

"I've stepped up into the firing line, I suppose you'd call it, and I'm quite good at it, I guess. I know how to do a bit of research here and a bit of questioning there and so on."

Mr Hodgson's hounding of ministers is "just a job" to him and nowhere near as enjoyable as being in Government.

"I'm pleased I've held some people to account. I suppose equally I think I've failed to hold Key to account over his blind trust that wasn't blind."

Now, he thinks the opportunities to land telling blows on the Prime Minister are closing. "I think Key has started to tidy up his own affairs."

As it goes, Mr Key last week again sent press gallery journalists bottles of "JK" pinot noir - from the Highwater vineyard the PM is not supposed to know whether he owns or not, and which was central to Mr Hodgson's allegations against him.

"That stuff is a bit careless but I won't get back into it," Mr Hodgson says. "His blind trust is starting to get a bit more opaque to me and I think that's good, because if it's opaque to me it's at least supposed to be opaque to him."

He has found flinging mud at a politician as popular as Mr Key has its downside. "In politics if you hold someone to account who is popular, blowback is common. [Mr Key] is historically popular and so the blowback is difficult, but then the blowback is part of the job."

But that's something 60-year-old Mr Hodgson won't be dealing with for much longer. He is leaving Parliament "to contemplate another sort of passage of my life before I get beyond that" and because he doesn't want to "overuse the generosity of my family".

The Whangarei-born and -bred former veterinarian and physics teacher - who moved to his current base of Dunedin many years ago as "a result of assorted women" - entered Parliament in 1990.

He held a total of 14 ministerial portfolios during his nine years in Government and wants to leave on his own terms "when people thought it was, if anything, a little early rather than a little late".

He believes some friendships with National MPs will stick after he goes.

Clearly they must be National MPs with clear consciences. "If there's anyone else silly enough to go around breaking the rules or ... damage the corruption-free nature of our society ... I'll come straight after them."

Hodgson's hits:
Richard Worth - Resigned as a minister and then from Parliament in June last year following a string of allegations around sexual impropriety and business dealings.

Bill English - Suffered embarrassment and repaid $11,000 after facing scrutiny over his ministerial accommodation subsidy.

Pansy Wong - Resigned from Cabinet and then, last week, as an MP after Mr Hodgson's allegations around misuse of the MPs' travel perk by her and her businessman husband.

And a miss:
John Key batted away Mr Hodgson's allegations that the Prime Minister's "blind trust" was in fact transparent.