Prefabrication is a hot topic among architects at the moment. Complete big housing developments are being built of readymade room units clicked together like Lego. Pyne and Howe are taking this thinking and applying it to a different market. M-house is designed from scratch - it's not an adaptation of any existing product - and it is not designed to stack up into anything bigger. Otherwise, it wouldn't be a caravan, would it? Mind you, you could cluster several of them together and make a congenial mini-village of them. In which case, as Pyne points out, you would not be a developer. You would officially have to get a licence as a caravan park operator.

Having made his pricey prototype, Pyne is investigating less labour-intensive construction methods for subsequent models, perhaps using a steel frame to bring costs down. But it will still be the Rolls-Royce of the trailerpark world. Though Pyne sees his enterprise as more akin to Morgan cars - handbuilt to order, with demand, when it comes, presumably managed through a waiting list.

So - is it a house, or is it a caravan? It is the latter, legally. And not only legally. "We wanted to achieve something that still retains some sense of it not being a permanent house," says Pyne. "We chose plywood on the inside walls, for instance, to show it's a different sort of animal. A bit like a cabin."

But a luxurious cabin. As Howe says, "It's way over base standards of conventional development at the moment. It's almost recklessly generous." Other architects' attempts to move into the trailer-home market - including a 1950s design by the famous American architect Frank Lloyd Wright - failed because, Pyne and Howe believe, they either looked too much like trailers, or too much like houses. Getting the balance right is tricky. But this one betrays its origins simply because, like all others of its kind, it is perched up high above its wheel-bearing chassis. You have to mount steps or a ramp to get in.