There's no need to move house if you outgrow your home, just buy the one next door. James Sherwood meets some of the colonists who are marching onwards, upwards and into the sky.
There was a time when, if you outgrew your home, you simply sold it and bought a bigger one. But a dearth of decent large houses on the market has led to a cunning new trend in property - colonising. Now residents with cash and panache are buying the flat upstairs or the house next door, bulldozing the walls and stretching out. A modern equivalent of The Beatles walking through four front doors into a giant groovy pad? Well, not quite. But given the ingenious ideas of these home-owners, it's probably only a matter of time. With enough capital - and accommodating neighbours - lofts can be colonised and even terraced houses can be turned into a giant superspace.

Dr Adam Lawrence and his wife Bobbie acquired the property next door to their 1830s terraced home in south London and enlisted the help of architect Peter Wadley, who spent 12 months converting the two properties into one house. "It was an ambitious project," says Wadley, who once lived in the same row of houses. "I did incorporate into the design brief the option of changing the conversion back."

The Lawrences now have three sons; at the time of the conversion, they had two and a desperate need for more space. "These houses were essentially built for poor people," says Adam, "the people who serviced the big houses across the river or who worked at the Royal Doulton factory at Lambeth Bridge."

The original property had been heavy-handedly modernised in the Sixties. For example, the fireplaces had been blocked-out and original features smoothed over. By contrast, the house next door had hardly been touched since the 1830s.

"Primarily, there was a mighty thick brick wall that needed knocking through," says Adam. "Then Peter Wadley had the idea of removing one of the staircases and building a gallery. We knocked through the wall dividing the hallway, knocked arches through on the first floor and converted the kitchens at the back into one big dining room." Peter Wadley's masterstroke was to extend the house into the garden then build a first-floor glass house on top of the new extension.

The Lawrence conversion is not seamless. As Adam says: "We are below sea level here. The entire terrace is built on wet clay, so, inevitably, the two houses are not even. You can see the hall floor gently rises from one property to the next. The ceilings are not quite level." To the naked eye, this is not obtrusive. The garden was a great success. "Each plot was on a different level," says Bobbie. "One side was covered in concrete and the other was a tip. Adam levelled the land out himself."

Kaffe Fassett, designer and author, has single-handedly colonised all three floors of his north London home. "It was total necessity," says Fassett. "I like to think of my home as the back lot of 20th Century Fox. It is a totally fluid space: a mobile studio where I work on my fabrics, paintings, mosaics and patchwork." To call Fassett's interior a riot of colour does not do it justice. Every inch of space has been photographed for one of Fassett's many books or looks like a mobile reference book of design past. Then there are the Gaudi-esque mosaics and his collection of china Buddhas ...

"I started with the middle floor," says Fassett. "Then the top floor became available because the people living there wanted a whole house and knew I wouldn't sell, so decided to move elsewhere. My business partner lived on the floor below me and he eventually accepted I needed more room. I'd always coveted his garden anyway. So he sold and I had the property to myself."