Time called on drivers over the limit: A 1.6m pounds campaign was launched yesterday to deter summertime drink-drivers. Christian Wolmar reports

THE TUBBY CHAP in the blue Dior casual shirt had already endured one disaster. His horse had come sixth at Windsor races and now he was having to blow into a breathalyser tube because a police patrol had noticed him driving while using his mobile phone and not wearing a seat belt.

He had to face a long wait because he had downed his last drink just before leaving the racecourse and breath tests cannot be taken within 20 minutes. His wife, sitting with him in their Range Rover, spent the whole time berating him for having had that last drink.

He blew into the tube and it quickly went to orange. He sweated while waiting for the mandatory 40 seconds, but it stayed there. Only if it goes through the orange-red phase and to the red one alone does the driver get arrested and taken to the police station to blow again into a more sophisticated machine.

Constables Daren Courtenay and Danny Skinner were on the late shift, 4pm till midnight, covering Maidenhead, Slough and Windsor and a chunk of the M4 and M25 motorways. They had decided to check the traffic streaming out of Windsor racecourse as the meeting ended.

PC Courtenay, young, keen-eyed and confident, looked for any minor infringement to allow him to stop a suspect - a car not giving way at the roundabout, a broken exhaust, excessive speed and so on. Actually, the powers for random searches are already there. The police can stop anyone to ask for documents and PC Courtenay watches out particularly for high-performance cars as these are so often stolen.

They sheltered in their Vauxhall Senator down a side road off a roundabout and occasionally hared off after a suspicious vehicle, sometimes stopping it, sometimes not bothering if the driver was behaving. They dispensed lots of advice and warnings, but no tickets, not even to the young man in a Suzuki Swift who was both speeding and overtaking on the inside.

PC Courtenay said: 'It is much better to give them a warning and send them on their way. Hopefully, they will be more careful.' And, of course, it means less paperwork, less time in court, less hostility to the police and more time spent on patrol.

The real quarry is the drink- driver. As pub chucking-out time approached, they stepped up the number of stops - a speeding Ford Granada, a BMW and a man who has got lost - but not a whiff of alcohol among them.

Then, just as we are about to pull into a garage to buy a drink - soft, of course - a Mercedes speeds by at 100mph, almost losing control on a bend. We give chase and stop it.

The driver was calm at first but then became agitated. He said he had had 'one cup of beer', but he reeked of alcohol.

PC Courtenay asked him to blow into the tube, but twice he just puffed on the outside. He was warned that he would be arrested if he failed to blow properly again. Again the pressure was insufficient to light the machine.

In the car, the man's stumbling English got worse as he panicked and begged for one more chance: 'You are going to ruin my life.' He was a manager in a local computer firm and clearly faced losing his job as well as his licence. PC Courtenay handled the situation calmly, explaining carefully that he did have one more chance, but only at the police station.

The man protested: 'You are mistreating me because I am a foreigner. Will my licence be cancelled?' Only if you are over the limit, PC Courtenay said.

He was led down into the depths of Maidenhead police station, next to the cells, where there is a Lion Intoximeter 3000, a high-tech breathalyser. After the paperwork was completed, he was told to blow into the tube to provide two specimens. If the lowest score was over 35, he would be prosecuted.

The man had two minutes in which to provide the specimens, but again he twice failed to blow properly. PC Courtenay warned him that one more failure would mean automatic loss of his licence. This time he succeeded and the score was only 14, well below the limit.

It was now 1am, an hour into overtime, but the two constables were satisfied: 'He won't be driving at 100mph after drinking beer again,' PC Courtenay said.

(Photograph omitted)