There's a plain-clothes dilemma at the front door: Harriet Hammond wanted to help the police catch a burglar, but her son was not so sure

THE DOORBELL rang and through the spyhole I saw a tall man in jeans and a leather jacket with medium-length hair and a small moustache. Even I, a total stranger to the world of crime, had a hunch that he was a plain-clothes detective.

I was right. After showing me his identity card, he came in and explained his business. It seemed we lived opposite a burglar - or at least, someone he and his police colleagues suspected was a burglar. And because of a new policy in the force the detective was proposing to install himself in my teenage son's bedroom, peep through the curtains at the man in question and then follow him to various crimes and catch him red-handed.

This is the new policy of proactive policing - as opposed to reactive policing, which means turning up hours after a burglary has taken place, taking endless notes and fingerprints and nine times out of ten not catching the culprit.

It sounded fine to me, but when I proposed the idea to my son he wasn't nearly so keen as I was to play decent citizen. 'What if I get beaten up?' he asked.

His fears were not unfounded. A few weeks ago a lawyer friend two doors down reprimanded a small boy he found tearing branches off trees in his garden. That evening he opened the door to the boy's father, leading an enormous gang of cool dudes with portable telephones. They proceeded to kick him from one end of the street to the other.

It was only because the lawyer happened to be a philanthropic chap who keeps an ex-con in his basement that worse harm wasn't wreaked on him; as it was, his jaw was broken and he had to eat through a straw for two months. My son, judging that the suspected burgler opposite was from a similar mould as the gang that had assaulted our friend, naturally did not want anything similar to happen to him.

The alleged burglar, or 'Chummy' as the plain-clothes policeman called him, was someone we had noticed over the years. A lonely little chap, we often caught him sadly staring from his window into our house as we played Scrabble or fooled about in front of the telly.

He never seemed to go to school. Social workers came and went. As he grew up, according to the detective, he gained a reputation for terrorising smaller boys and stealing their bikes. More recently he was thought to have been responsible for a series of major robberies - just the kinds of robberies that I, as a responsible member of society, would like to help prevent. I tried to compromise with my son. The policeman would watch from my room, not his. This did not have the reassuring effect I had hoped it would.

My cleaner actually asked why we had a plain-clothes policeman visiting us so often - he had taken to popping round daily to try to persuade us to co-operate - so it was obvious that anyone who saw this casually dressed individual standing at our door knew his profession instantly. Chummy opposite was probably already putting two and two together. I wrestled with a moral dilemma. The only answer was to share it.

From my room a large tree partly obscured the view of Chummy's flat, so I suggested that the police should do their surveillance from our house and from next door on alternate days. As luck would have it, next door had a room with a view to let, and we were never bothered again. The police set up camp there

instead.

In the event I was relieved of making a difficult decision - between setting a good example to my son in helping the police to prevent burglaries that we would both hate to have committed on us, and protecting him from a potentially vicious attack - or the fear of one - by a gang of Chummy's mates, whom we saw regularly hanging round Chummy's house in the latest pounds 200 trainers, gold chains and all the paraphernalia that scream: 'Money made from extremely dodgy sources]'

It was a decision that I could perhaps have taken for myself, but whether to take it on behalf of a child was another matter altogether - and one to which I still do not have the answer.