My mother and father are driving me frantic: He's 83 and ignores his diabetes; she never goes faster than 35mph. A daughter explains the problems of parents who refuse to leave the road

Our three-row family estate car was packed to the gunnels with children on a holiday outing. We were driving down a moderately busy main road when an elderly driver came like a bat out of hell from a side road on our left. He swung violently to the right, caught up with and crashed into the rear of a lorry travelling towards us, and bounced in spectacular kangaroo-style hops back across the road.

The old man's car was a write-off; the lorry sustained no visible damage; fortunately, the drivers were merely shaken, not injured. In addition to the accident, I suspect I had also witnessed the final chapter in the driving career of one old age pensioner.

My father and I experienced a crunch of a more personal nature last year. Dad is 83 and diabetic. He treats his diet with the same cavalier abandon he treats the rest of his life . . . which is what makes him so appealing, outrageous and fun to be with. His is a character combination which results in a refusal to age gracefully, let alone acknowledge old age, or consider stopping anything he still believes himself capable of. And it's probably why he's such an independent octogenarian with a zest for life.

So it was no surprise when, last summer, he proposed a short holiday with his grandson for company. The trip would involve driving more than 350 miles, negotiating motorways and city traffic he was unused to. Worried, I suggested they travel by train. 'So much more interesting and relaxing,' I enthused.

It was like a red rag to a bull. I was told not to worry and fuss, I was told his reflexes were as good as ever, and, when I finally refused permission for my teenage son to go with him by car, my concern was labelled 'criticism' and 'dictatorship'. Both of us were upset.

I know grandchildren are so precious that grandparents are all the more careful with their valuable cargo . . . so careful in my mother's case that she drives no faster than 35mph. Since she rarely looks in her rear-view mirror, she remains blissfully unaware of the long row of drivers queuing up behind. Thankfully, or perhaps not, she doesn't seem to notice the uncomplementary gesticulations which often accompany a plume of exhaust smoke as an overtaking vehicle snakes off into the distance.

In contrast, and lest anyone think I am ageist, my husband's father is also 83 and drives thousands of miles each year visiting friends all over the UK. He drives lawfully fast with efficiency and courtesy. He's welcome to drive me, or the kids anywhere, anytime. He'll blow the whistle on his own driving career the minute he is less than capable. He's that sort of a chap.

Driving equates with independence. I am sympathetic to my parent's needs: a car to do the shopping, to see friends and family. I am also conscious of the good they put it to. They visit the housebound, they organise lifts for less mobile friends to and from hospital.

They make life more pleasurable for friends unable to use, or perhaps afford, public transport by taking 'little trips'. Those of us who live life in the fast lane can fail to appreciate the delight a few miles ramble in the car to a pretty spot can bring to those virtually housebound.

I've now told my parents that I am only willing for them to travel locally with their grandchildren, but to tell them to stop driving completely would be an emotional minefield for all concerned. I've advised them to no longer travel long distances, to stop night-time driving (when they have particular difficulty), but it's advice they don't wish to heed.

As they're always pointing out to me, they've never had a bad accident. The trouble is, I don't think the final whistle will blow until they do.