It started as farce. A teacher who’d been on a pre-Christmas drinking session with colleagues was told off by a police officer for urinating in the street as he made his tired and emotional way home. His companion, a teacher at the same Essex comprehensive, initially tried to shut him up when he began shouting abuse at the officer. It ended in tragedy, as Chelmsford magistrates last week sentenced Michael Feeney, 32, and Mark Jones, 28, of The Boswells School to four months imprisonment for assaulting 26-year-old PC Matthew Turner.

There was a moment of pure, silent shock as the smart-suited teachers, who had pleaded guilty, were led away in handcuffs to begin their sentences. The stricken face of Mark Jones’ wife, Marianne, also a teacher at The Boswells, spoke volumes. Chair of the bench David Lucas said the offence - “an unprovoked attack on a lone police officer” - was so serious that custody was the only way of dealing with it. The teachers were each ordered to pay pound;300 in compensation to PC Turner, and pound;60 costs. Two months of the four-month prison sentence were suspended.

But the real punishment for both men is likely to be loss of their careers. “Mr Feeney will undoubtedly lose his employment,” said his solicitor, Roger Brice. “And he suspects it will result not just in the loss of the department headship but in considerable difficulty in his career from now on.”

Both men have taught at The Boswells, a popular and high-performing grant-maintained school, for the past five years. Headteacher Kevin Arkell announced immediately after sentencing that “the school will carry out an immediate and thorough investigation of all the evidence involved to ensure that appropriate disciplinary action is taken against each member of staff”. The pair have been suspended since last December.

Much was made during sentencing of the two men’s profession. That morning, a bevy of newspaper photographers and film cameramen clustered in the bright spring sunshine on the steps of the court. Inside, the press seats were full to overflowing. Jones’ solicitor, Stephen Chesney, speaking in mitigation, said the interest was due not to the nature of the offence but to the nature of the offenders. “They are unlikely offenders, because they are teachers.”

In Chelmsford last week, the role and status of teachers was under sharp and unwelcome scrutiny. A local journalist remarked that the case was “a gift” to her paper - this would not have been true had the two been plumbers or postmen. There was a dark irony in the way it took the unpleasant events of the early hours of Saturday December 13 to focus attention on the way teachers are still almost automatically regarded as upstanding members of the community.

And indeed it would be hard to imagine a more unlikely candidate for the role of hooligan than Mark Jones. In court, Jones - head of chemistry at The Boswells - was a picture of contrition. A slim man with short, pale hair and dark-shadowed eyes, he twisted his wedding ring, sneezed into a white handkerchief and sat before the trio of magistrates in an attitude of misery. But it was he who made the first lunge in the fateful scuffle.

The court heard that the lone policeman had seen Feeney urinating in the street at 1.20am and reprimanded him. Both men were abusive and shouted:

“Haven’t you got anything better to do?” They were told to go home quietly. Half an hour later, they again ran into PC Turner as he reprimanded two other men for urinating against a wall. Feeney shouted at the officer: “Are we criminals for urinating in the street? Are you a bloke? Don’t you take a piss in the street now and then?” Jones, according to the PC’s evidence, tried to calm him. But when PC Turner moved to arrest Feeney for being drunk and disorderly, Jones grabbed his radio mouthpiece. The two teachers then set about the officer in what PC Turner described as “the most frightening moment of my career to date”. He lost his glasses and helmet and was kneed in the groin. He managed to move towards a spot where he knew a closed circuit television camera was filming, and, as a bystander intervened, the end of the fracas was caught on video.

In court, Feeney, stocky and with dark, curly hair, showed less evidence of remorse. He looked at the press frequently and with an aggrieved scowl as if it was he who had ended up in hospital that night with swollen testicles, bruised thighs and his spectacles broken. It emerged in court that he had a previous conviction, for threatening behaviour, acquired in 1992. Still, it was clear that neither man is routinely violent and both have been adequate, possibly excellent, teachers.

Forty per cent of all violent crimes involve drink says the Probation Service and this was one of them. The drunken scuffle in December was described convincingly as a moment of madness by Jones’ solicitor. “Mr Jones lost control for a couple of minutes and in so doing acted totally out of character,” he said. He brought up the stress of teaching, saying it was “the end of the penultimate week of what is the longest and most stressful term of the academic year”.

Despite the shock of seeing teachers go to prison, sentencing was not harsh. Attacks on police officers are taken extremely seriously and magistrates have a guideline for such cases - the suggested penalty is six months imprisonment (the maximum magistrates can hand down) andor a heavy fine.

Chelmsford town centre is no stranger to such incidents. The city council installed 50 closed-circuit television cameras two years ago, in a bid to reduce the fear of crime. The centre is dominated by shops and offices and described by one local resident as “not owned by the people of Chelmsford”. People come from out of town to party at the clubs, pubs and restaurants like the Chicago Rock Cafe, where the teachers had been drinking before the assault. Large and airy, it boasts wicker chairs, potted palms and sepia-tinted photographs, the mock colonial effect spoiled only by the view of the Co-Op opposite. Describing itself as strictly for the over-20s, it is a reasonable place for teachers to choose to let their hair down.

The Boswells is four miles away, in the north-east of the city, and draws its pupils mainly from the surrounding suburbs and villages north of Chelmsford. In the character reference provided by head of science Keith Feeley, Mr Jones emerged as a dedicated teacher with the respect of pupils and colleagues. Informally, on the neat avenues and cul-de-sacs around The Boswells, a similar view emerged. “Mr Jones is cracking - brilliant,” said a sixth-former. “Nobody’s knocked them for their teaching skills,” said the mother of a pupil at the school.

But behind the nets in the neat semis and bungalows, sympathy for the two men was limited. “They did something wrong and they should pay for it,” said Hilary Alderman, whose daughter starts at The Boswells in the autumn.

“I couldn’t believe it,” said one local resident and former pupil who preferred not to be named. “It’s a good thing they’ve been sent to prison. They’re supposed to be setting an example to our youngsters and this is not a very good one.”

The Boswells is over-subscribed and has, until now, enjoyed an excellent reputation. Inspected in 1996, the 1,500-pupil comprehensive was described as “a very good school with some outstanding features”. The inspectors said: “Teachers and other adults in school provide good role models.”

Kevin Arkell, headteacher at The Boswells, was clearly feeling the strain last Friday. He said, in no uncertain terms, that he did not expect The TES to be asking questions.

In truth, the school’s reputation in the community is not at stake. Parents The TES spoke to see the incident as an isolated one, not a reflection on the school. There is concern though about the message sent to children. “A lot of jokes are going round about peeing up walls and teachers bashing up policemen,” said one 45-year-old woman with a child at the school and another about to begin there. “The consensus is that what they’ve done is pretty horrifying. I’m worried that if the teacher has done it, the children might think it’s acceptable.”

After a hostile encounter with the head, I was glad to leave the locality of The Boswells. The taxi driver who picked me up has a teacher friend working there. He took a sanguine approach. “At the end of the day the Government has to take some responsibility for retiring all those experienced, mature teachers and overloading all the rest,” he said. “They all feel as if they’re in a goldfish bowl. The pressures are immense.”