Politicians running for election will have to tone down personal attacks on their opponents after a former Labour minister was barred from the Commons for three years for making false claims about his electoral rival.
In a landmark ruling, two High Court judges said that Phil Woolas, a former immigration minister, broke election law with statements he made in a pamphlet and two newspapers distributed in the final stages of May's election.
They found that he had attacked his LibDem opponent's conduct and character with statements that he courted Muslim extremists who had advocated violence against the Labour MP.
They ordered a re-run of the election contest for Mr Woolas' Oldham East and Saddleworth seat and banned him from standing as an MP for three years. He said yesterday he would take the decision to judicial review.
Last night election experts said all political parties would have to reassess the often very personal nature of British election campaigns in the light of the ruling, for fear of being challenged by their opponent in the courts at a later date. Dennis Kavanagh, professor of politics at the University of Liverpool and author of The British General Election of 2010, said: "This is yet another example of the judicialisation of politics. In the past the courts would never have become involved in a case like this but we are now much more like the US in that regard. In future, politicians will have to be much more sensitive to the accusations that they make."
More immediately, a potentially awkward by-election looms for both Labour and the LibDems. Ed Miliband will hope to capitalise on Coalition unpopularity after the spending cuts announcement – but could face a backlash from voters angry at the party's perceived "dirty tricks".
Mr Woolas, who only won his seat by 103 votes, was immediately suspended from the Labour Party and Deputy Leader Harriet Harman said there would be no appeal. "It is no part of Labour's politics to try to win elections by telling lies," she added.
But Mr Woolas's solicitor, Gerald Shamash, said: "Those who stand for election and participate in the democratic process must be prepared to have their political conduct and motives subjected to searching scrutiny and inquiry," he said.
"It is vital that those who make statements about the political character and conduct of election candidates are not deterred from speaking freely for fear they may be found to have breached electoral laws."
The court heard that the strategy Mr Woolas and his team concocted to deal with the perceived LibDem threat was described even by them as "risky". Diary entries kept by Mr Woolas, later published in The Independent, showed he thought he was going to lose.
The court heard that false statements were made in three publications on behalf of Woolas in the last few days before the election. His team had set out to "make the white folk angry" by depicting a campaign by Asian extremists to "take Phil out" and present Mr Watkins as being in league with them.
They also falsely stated that Mr Watkins had committed offences by spending more than the law allowed on election leaflets, and had broken a promise to move to the constituency.
Giving their judgment, Mr Justice Nigel Teare and Mr Justice Griffith Williams said Mr Woolas was guilty of illegal practices under election law. He was ordered to pay £5,000 to Mr Watkins, the sum he paid to the court when he launched the petition. He will also have to pay the costs of the case to the petitioner. Under the Representation of the People Act 1983, the judges' report must also be passed to the director of public prosecutions, opening the prospect of a criminal inquiry.
Speaking after the verdict, Mr Watkins said: "The idea that if you lie about your opponent and you know you have lied about your opponent then simply you have no part to play in democracy. I think this decision will help clean up politics."
Commons Speaker John Bercow will announce on Monday whether there will be a by-election for Oldham East and Saddleworth now or whether to wait for further legal proceedings.