Constable Donnelly, who fronted the PSNI/DoE campaign Smashed, which warned of the dangers of driving while under the influence of drink or drugs, was herself later caught drink driving.

She was fined £120 and banned from driving for a year - but yesterday it emerged she had held onto her job.

Yesterday, PSNI deputy chief constable Paul Leighton defended Ms Donnelly's return to work - despite his earlier assertion that in most cases officers would lose their jobs if convicted of similar offences.

He said that drink driving was wrong, but pointed out that the incident involving the woman police officer preceded the PSNI's dismissal policy of May 2006.

However David Lyle, head of Lyle Bailie International, said: "We are embarrassed by this situation, as I'm sure are all the dedicated police officers who, over the years, have helped us make these ads.

"Here, in the case of Constable Donnelly, we had someone who had put themselves forward to represent the police in this ad - and subsequently let them down."

Mr Lyle added that he feared that Constable Donnelly's conviction could adversely affect the seriousness of the campaign's integral message.

"I have no doubt a police officer being convicted of drink-driving weakens the 'never, ever, drink and drive' message - and that is my main concern," he said. "I give no credence to any sense that there are mitigating circumstances for drink-driving."

He added that any member of his company disqualified for drink driving would be sacked - and he called for a Policing Board review as to why this did not happen within the PSNI.

Smashed, the ad fronted by Constable Donnelly, had been aimed at increasing awareness of drug-driving issues with the slogan, You'll get smashed if you drive on drink or drugs.

The court heard how her car was in collision with another car on Bangor's Gransha Road. She had 140mg of alcohol in 100ml of blood. The legal limit is 80mg.

In May 2006, Mr Leighton warned any officer breaking the law would be sacked or forced to resign.

But, as the row over Constable Donnelly's return to work erupted yesterday, he said there are circumstances which may merit a relaxation of the rules.

"Since we made our policy statement in May 2006, any case post that date that has come to hearing, the officer has been either required to resign or has been dismissed," he said.