Claims that a controversial by-pass route "disappeared off the agenda" because of Liberal Democrat influence has provoked a furious row.

Former transport minister Tavish Scott yesterday spoke of "outrageous mud-slinging", while leading LibDem donor Ian Suttie threatened legal action if anyone suggested he had acted improperly.

The row erupted after campaigners against the current Aberdeen by-pass plans produced evidence that Mr Scott had met a group called Pitfodels and Cults Conservation Group in October, 2005.

They claimed that after that meeting the option to take the relief road through that area was dropped.

Mr Suttie, a major donor to the local constituency party of LibDem leader Nicol Stephen, was behind that local conservation group, campaigners claimed.

But Mr Suttie countered last night that he had never met Mr Scott.

Mr Stephen refused to comment directly yesterday but Mr Scott issued a furious rebuttal, also denying that he had ever met Mr Suttie.

As opponents of the Aberdeen ring-road project said they were considering a referral to the Standards Commission, arguing that party funding may have influenced decisions, LibDem aides played down any link between a major donor and an abandoned route which passed within a stone's throw of his house.

The Road Sense group had been forced to step outside Holyrood yesterday in order to air their concerns, because the parliamentary authorities ruled that they could not use the building to criticise sitting MSPs.

The campaigners against the Aberdeen Western Peripheral Route, went on to make a powerful series of claims based on documents they have secured under freedom of information. They accused the last government of choosing a final "hybrid" route without costings or consultation, claimed there are still no new costings, and said that as a forthcoming local public inquiry will be unable to look at the original decision-making process they reserve the right to invoke judicial review.

They also claimed costings have never been updated over a period of several years and that these must now be approaching £600m, a figure once condemned by ministers as unacceptable.

But it was the claims about Mr Scott's meeting on October 7, 2005 that caused ructions. The protesters had secured details of the transport minister's diary, showing his meeting with the Cults and Pitfodels Conservation Society. Road Sense claimed that local millionaire Mr Suttie had been involved in this meeting.

They also assumed Mr Stephen must have been present and thought Mr Stewart Spence, proprietor of the nearby Marcliffe Hotel, was also present, which he denied last night.

This unravelled further when Mr Stephen said he was not at the meeting and Mr Suttie later claimed he had never met Mr Scott.

But Road Sense insisted last night that they believed Mr Suttie was closely involved in the group the transport minister met that day, whether or not he was present in person.

Mr Suttie said: "I have never considered the proposed Pitfodels route had any merit due to its proximity to Aberdeen.

"I consider these allegations to be without foundation and defamatory and will not hesitate to take all steps necessary to protect my good name."

Mr Scott said the meeting in his ministerial diary involved several groups, not just the one from Cults, and accused the campaigners of "outrageous mud-slinging" to cover up the way they were at odds on the by-pass issue compared to mainstream political opinion.