LIZZIE knows all about summer holidays with stepchildren. During the first years of her second marriage, they were explosive, difficult and horribly instructive. With three of her own children and two from her husband, Harry's, previous marriage, diplomatic relations broke down on several occasions. 'One problem was that my children were aged 10 and under - still young and enthusiastic about everything - and Harry's two were teenagers and obviously wanted to do different things.'

For stepfamilies coming together infrequently, or only at holidays, the summer can be an especially stressful time. Enormous effort and emotion are invested as children of past and present marriages struggle to present a happy, united front. The National Stepfamily Association has just published a Summer Holiday Survival Guide. Lizzie could have done with it.

During their first summer holidays together, Lizzie, whose children and stepchildren are all adults now, remembers being too hard on Amy, her 14-year-old stepdaughter, and Peter, her 16-year-old stepson, both of whom went to boarding school. 'We stayed mostly at Harry's house in the country, which they and my children loved. But Peter was very rude and banged doors, and he had a motorbike - which I detested.

'I tried to organise things everyone would enjoy, but often they didn't work. There was a terrible row when we found Peter, near drunk, under the table in the bar at a local country fair - we thought he had gone to do the wellie-throwing competition.'

On one occasion Harry and Lizzie insisted that Amy come down to the house in the country for a long weekend, instead of staying in London, where she wanted to go to a party. 'She sobbed and sulked throughout the journey and collapsed under a tree by the sitting-room window all Saturday, sobbing every time someone went past. We all thought it was quite funny, but it wasn't resolved until Harry's ex-mother-in-law got involved. In retrospect, I think we ought to have let her go to the party.'

Lizzie soon discovered that it was better to spend the holidays on neutral ground. 'This was a breakthrough for all of us, especially if we chose somewhere new and if I managed to find at least something to amuse each person,' she says. This meant a beach for her children - Belinda, aged 10, and the twin boys Simon and David, aged 7 - riding stables for Amy, tennis courts for Peter, and fishing for Harry.

Harry's children would spend half their holidays with their mother and found the change-over difficult. They would arrive with stories of staying up late for dinner or going somewhere unusual. 'The last thing they wanted was to stay in a cottage, having supper with three small children. Obviously we had to play it their way a little, but we were careful not to get involved with the competitive bit of who gave them the best holiday.' Lizzie admits she was tougher on her stepchildren when they first arrived from their mother.

This changing over caused a furore in the early days. Amy, having just returned from the Bahamas, joined the new stepfamily on a holiday to Dorset and would not stop complaining. 'I know Swanage beach does not compare with the Bahamas, but I was damned if this girl was going to ruin our holiday with her moans about it being too vulgar, too windy, there being too many people and how glorious it had been with her mother.'

Amy excelled herself in rudeness, says Lizzie, while she herself tried to amuse everyone and felt tight-lipped. By the end of the day tempers were boiling, but it was Harry who erupted first, over a missing stud to a camera strap.

'Harry started shouting that he couldn't put anything down without it being tampered with, and that Simon must be to blame because anything he touched always broke. Just for good measure, he added that he hated Swanage beach and sandwiches with sand in them.'

A massive argument ensued. 'I said: 'Look, Harry, my children are perfectly well disciplined by me and I don't need any help from you. Your daughter has behaved like a beast all day and you have said nothing to her. Now you and Amy can get out, drive back to London, and leave me here to enjoy the summer. If you don't go then I and the children will leave.' Harry was stunned, and I know I reacted far too strongly. We have had three catastrophic rows in our 20 years together, and that was one of them.' Neither left and the holiday improved, but cautiously.

Afterwards, they found out that Amy's holiday with her mother had been terrible. 'Her mother had been on a drinking binge and had locked herself up for days while the child was left with a maid sitting on the veranda. I had to be very loving and charitable afterwards.'

She chastised and questioned herself about how fair she was being to her stepchildren, and realised that her relationship with Harry significantly altered when his children were staying.

'It wasn't easy, but I had to be big-hearted and generous. I told myself that when there were clashes I had a duty towards them not to score goals. Teenage children are not adults, they are weaker than you, and whatever happens will have a far greater impact on them as young, impressionable people than me as an adult.'

As the summers rolled by, matters improved and relationships began to develop between the children and Amy; Peter had grown too old for family holidays and even today remains fairly distant. 'Even though Amy hated being woken too early by the chlldren - and I know two little boys of nine can drive a 16-year-old mad - we started to share some happy times, and once you can do that then some problems can be solved.'

They chose a villa in Malta together, and holidays there were a success. 'The children had some escapades - Amy once bought them glasses of shandy, the boys were only 10, but I let things go.'

Looking back, Lizzie feels that being frankly determined to have a good summer holiday herself was another good survival strategy. 'For me it meant insisting on brutal honesty all the time in order to clear the air. I like to get things straight and was always asking: 'What did you mean by that?' Harry's children found that quite difficult, but mine were used to it. If you allow things to fester then they get worse.'

All the names have been changed.

National Stepfamily Association, 72 Willesden Lane, London NW6 7TA.