The SNP Government was last night embroiled in a dirty tricks row after an aide to a senior minister quit over smearing political opponents on the internet.

Mark MacLachan, who worked in Constitution and Culture Minister Mike Russell’s constituency office, had attacked rivals on his blog since February.

The row threatens to undermine Mr Russell’s launch tomorrow of the Scottish Government’s White Paper on an independence referendum.

Mr MacLachlan suggested some Labour politicians got a sexual thrill from bullying women, branded a prominent Tory “the biggest liar in the Scottish legal system”, and posted a picture of Gordon Brown in a noose with the headline “duplicitous lying bastards”.

He also alleged a married Labour MSP visited gay cruising spots, badmouthed the daughter of Lord David Steel, the former presiding officer at Holyrood, and described several opponents as “c***s”. Mr MacLachlan had been employed at public expense since 2007.

For years, there have been complaints about extreme attacks by SNP supporters, or “cyber nats”, on the internet.

The row has echoes of the Damian McBride affair earlier this year, when Gordon Brown’s spin-doctor was forced out after he discussed setting up a website to smear prominent Tories.

Mr MacLachlan wrote his blog, “The Universality of Cheese”, under the pseudonym Montague Burton.

He called one Labour MSP “the laziest man in Scottish politics”, Falkirk MP Eric Joyce was labelled a “poisonous dwarf”, and Labour health spokeswoman Jackie Baillie was dubbed “Jackie the Hutt”.

Last week, he claimed two Labour councillors had a history of “malicious bullying and intimidation” of women.

Next to a picture of a man spanking a woman, he wrote: “Who knows what kind of thrills these chaps get from trying to bully and dominate the ladies?”

He also called an academic hostile to the SNP a “stark raving c***”, referred to “some odious c*** from the Labour party”, and called one journalist he disliked “propagandist c*** of the year”.

His blog has now been closed.

Last week the so-called cyber nat Bruce Newlands was investigated by his part-time employers after he repeatedly called Scottish Secretary Jim Murphy a “c***” on his now-closed blog.

In a statement, Mr MacLachlan said he deeply regretted his actions and unreservedly apologised to all concerned, and to Mike Russell.

“In getting carried away with my comments, which were very wrong, I have let myself and my colleagues down.”

Iain Gray, Scottish Labour leader, said: “The First Minister has to make clear if Mike Russell knew about his aide’s blog or not.

“This long-running hate campaign by the SNP has no place in Scottish politics but he has done nothing about it. Alex Salmond must act now. He has to clean up his act. As First Minister, it is his duty to personally apologise for this filth.”

Scottish Tory leader Annabel Goldie said: “The nasty underbelly of the SNP has been exposed. People are judged by the company they keep. Alex Salmond must order an independent review of all SNP Government staff and advisers to see if there are any other cybernats peddling such defamatory, gutter politics at the taxpayers’ expense.”

LibDem leader Tavish Scott said: “We need an apology from [Mr Salmond] and for him to disassociate himself from this blogger immediately.”

Patrick Harvie, Scottish Greens co-convener, said: “We have long warned the SNP that the cybernats would damage their reputation.”

A spokesman for South of Scotland MSP Mr Russell said he was shocked hear of the blog on Thursday: “He knew absolutely nothing about it, and has accepted Mark MacLachlan’s resignation.”