Two hundred and thirty-five days to Christmas, and counting. I’m not normally the kind of person to wish his life away, but events on the domestic front mean I really do find myself numbering the days. Why Christmas? Because that’s when I’ve told myself it’s realistic to expect to have a proper roof over my head again.

Let me rephrase that: I am incredibly lucky to have a lovely place to live. It’s just that, as a father of three who has recently married a woman with five children from her own first marriage, the definition of what constitutes a “proper roof” has shifted considerably. The woman in question is called Nicola Horlick, and she is a City fund manager – you may have heard her referred to as “superwoman”. We are part of that thoroughly modern phenomenon, the “jigsaw family” – a growing number of couples trying to provide a home for our two sets of children, if only for a few days of the week.

I had never expected that at this stage in my life, I would be living back in my old bachelor flat in picturesque, villagey Barnes, southwest London. The flat is a good size, with a spacious kitchen-diner, a light-filled living room, a large main bedroom, two other twee bedrooms and a second bathroom in the upstairs loft conversion.

It all seemed a great idea when we moved there from Nicola’s Knightsbridge townhouse in March last year. It was a good time to sell in central London, and we were prepared to rough it for a few months until our new home – a £3m, nine-bedroom new-build in Barnes – was ready.

The accommodation is perfect for a newly married couple (which Nicola and I still are – we were wed in September 2006), but it is not just the two of us. Nicola’s three youngest, Rupert, 14, Antonia, 11, and Benjie, 8, live with us full-time, which makes the place rather on the small side. Oh, and Nicola and I also need to provide a base for Alice, 19 (travelling abroad before attending university), and Serena, 17 (away at school in termtime).

Then we have my own children to consider: Patrick, 16, Jamie, 14, and Madeleine, 12, are in the excellent care of their mother, and live just two-thirds of a mile away from the flat. I see the children several times a week, and happily spend a large part of most weekends running them around to football matches, hockey and all the rest. With eight children in total, sleepovers, as you can imagine, are something of a rarity.

These days, almost half of marriages end in divorce, so record numbers of families are in the same position, with children calling two houses home instead of one. Despite our discomfort, we’re fortunate, of course. Although the building work has, inevitably, dragged on much longer than we expected, an end is at least in sight. We can look forward to the day when we will take possession of the house, with its cinema room, gym, guest house and large garden, where the boys and I can play football.

Others, though, can see no end to their plight. Relate, the relationship and sex counselling service, reports a steady increase in the number of jigsaw families coming in for therapy, needing help to negotiate a new home life – with new members.

“Not only do some children have to get used to others coming and going, they have to work out how to share the rooms and the space,” says Denise Knowles, one of the organisation’s family counsellors. “Both parents increasingly want 50% child custody if they are divorced – which is great – but they have to be able to accommodate everyone. Resentments can occur, and it can be complex.”

Knowles cites the case of a remarried couple with four school-age children – and just two rooms for them. Bunk beds were the only option, and not a popular one. “It takes a lot of understanding and negotiating to work these things through,” she says.

According to Relate, it is hard enough when it’s just the two of you moving in together, let alone your own children and someone else’s. And, if making siblings share is tricky, making those who hardly know each other can be nigh-on impossible.

With the housing market struggling to cope with expanding families and the extra demand for homes – Gordon Brown has already announced that 3m more houses will be needed by 2020 – it would be churlish to do anything other than make the best of things.

In our case, this has meant being resourceful and artificially extending the living space of the flat. We have taken a short lease on a studio office overlooking the Thames, just two minutes’ walk away. It’s a fantastic commute. The view is uplifting and always enjoyable – rowers and pleasure cruisers, as well as the herons that have come back to hunt on the riverbank.

This office is, in effect, my study. I’ve spent the past year there writing the sequel to my first novel, Meltdown. It also doubles as a storage room. The majority of our belongings have been in store for a year – and I’m pleased to say that I miss very little, so the charity shops can expect a bonanza when we do finally move to the big house.

The many restaurants in Barnes, meanwhile, have become an extension of our kitchen and sitting room, while the lack of a back garden is compensated for by membership of the Bank of England Sports Club, next to Richmond Park.

That doesn’t mean, though, that I am not longing for the day when I will have a proper roof over my head.

Meltdown is published by Macmillan (£10)

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