A leading lobbyist has been accused of "utterly reprehensible" behaviour including bullying and intimidating opponents.
Labour MP Thomas Docherty claimed Mark Cummings sent him a text message containing sectarian abuse after he opposed a development planned by one of the lobbyists' clients.
Mr Docherty, himself a former lobbyist, used parliamentary privilege to make a series of claims against Mr Cummings, director of Edinburgh-based Invicta Public Affairs.
The Labour MP for Dunfermline and West Fife told the Commons the police were called in over the text message, sent when he was a parliamentary candidate, but there were no charges.
"I am not alone in receiving intimidatory behaviour from Mr Cummings, he is well-known for bullying and becoming aggressive, particularly towards women opponents of schemes," Mr Docherty claimed.
But in a response issued through his solicitors, Mr Cummings said Mr Docherty's comments were "unfounded, false and defamatory", and challenged the MP to repeat them outside Parliament where they would not be protected by privilege.
Setting out examples of "unacceptable" practices used by Mr Cummings, Mr Docherty claimed the lobbyist would get an employee to pose as a journalist to sound out politicians about planning applications. He also claimed Mr Cummings placed candidates to stand for election to community councils in Scotland which have to be consulted on planning issues.
Turning to the dispute that led to the text message, Mr Docherty said he had opposed the Dunfermline development along with local residents. He claimed the text was "incredibly offensive" and contained the words of a sectarian song associated with supporters of Rangers Football Club.
"What was quite clear to me and to others in the community was the only reason why I had received this offensive and intimidatory text message was because I was currently opposing a planning application which he was pressing for," he said.
Mr Cummings said he would write to Commons Speaker John Bercow to complain about Mr Docherty's claims. The text message allegation was "entirely false", he added. He said: "Mr Docherty first made this allegation in 2009. I denied the allegation unreservedly at the time and repeat my position today."
