An attack on her political rivals has landed Watford Mayor Dorothy Thornhill in trouble with the Standards Board for England.

The Liberal Democrat mayor was found guilty of breaching its code of conduct after attacking opposition parties in a letter, written on Watford Borough Council-headed notepaper, which was sent to 891 residents.

However, she was judged not to have brought the council into disrepute.

The Mayor was writing to inform residents of her decision not to pursue plans to move Watford Indoor Market outside into the high street.

But in the note, signed by the Mayor and dated September 4, 2009, she said: “I hope in the time as your Mayor I have proved that I care about Watford and can manage difficult problems and challenges – we have come a long way since the old Labour regime made us a laughing stock in the local government world and we were branded nationally as one of the worst performing districts in the country.

“None of the opposition parties have cared about this issue prior to the Market Traders campaign. At best they are misinformed and misguided, at worst cynical opportunists with no real thought for the future of the town or your council tax.”

Following a complaint from Watford MP Claire Ward and a subsequent investigation, the Mayor was found to have “failed to comply” with the board's code of conduct. However, she will face no further action.

A summary of the board's report said: “While noting that Mayor Thornhill had legitimate non-party political reasons for writing to the local residents, the Ethical Standards Officer considered that a paragraph of the letter she sent consisted of a political attack on her opponents.

“The Ethical Standards Officer found that the political attack included in the letter was not characteristic of Mayor Thornhill’s style and noted her admission that it fell below her usual standard of communication with constituents on council business.

”The Ethical Standards Officer concluded that in using the council’s resources to draft and circulate the letter containing the political attack, Mayor Thornhill had used her authority’s resources improperly for political purposes...However, given the mitigating factors, the Ethical Standards Officer did not find that Mayor Thornhill brought her office or authority into disrepute.”

Section five of the code states: “You must not conduct yourself in a manner which could reasonably be regarded as bringing your office or authority into disrepute.” Section 6b(ii) says: “You must, when using...the resources of your authority ensure that such resources are not used improperly for political purposes.”

Despite the ruling, Mayor Thornhill said she stood by her comments but understood she shouldn't have written them on council-headed notepaper.

She said: “I am pleased that the Standards Board for England have recognised the unique situation I was in at the time of writing the letter and has recommended no action be taken against me.

“It was reassuring to hear they fully acknowledged the legitimacy of my letter and agree that it's party political content was relatively minor. The objection rested entirely on six lines in the final paragraph.”

Ms Ward “welcomed” the decision, which she said proved she was right to make her complaint.

She added: “I hope that Dorothy will now apologise to Watford residents for her actions.

“The fact she had to backtrack on her proposals shows that she's been forced to rethink because of pressure of market users and market traders and that's what we wanted, for her to listen and rethink the proposals.

“I hope now we're not going to see the market withering and I trust the council will be coming forward with measures to support the market in the immediate future and not just the long term.”