Diarmuid Gavin: Constant gardener

Hot tub, guest room, sauna – this may be just his London 'crash pad', but Diarmuid Gavin went to town when he designed the back yard

I moved to Willesden Junction, in north-west London from Ireland about five years ago, mostly because I had started to do a lot of work for the BBC. Initially, I'd rented a flat in Notting Hill and then eventually bought myself a little place in Kensington Church Street, but that didn't have a garden and I very much wanted one. It had this great big flat roof and I always dreamed of sticking a garden there, but I wasn't allowed to do so. I used it for parties instead.

I decided I wanted more of a home for me and my wife, and as soon as I saw this place I loved it. After I was shown around, the woman who owned it saw me out and then stopped to chat with her next-door neighbour, and I just like the idea of having nice neighbours. The house was in great nick, too, very spick and span, though I've butchered it since, but then I usually do with properties. It's not the 1930s any more, is my logic, so why do I have to remain true to its original design?

Here's a funny story for you. Shortly after we bought it, we were taking down walls and picking up floorboards. In the kitchen underneath the carpet there was lino and underneath the lino there was a lining of really old Irish newspapers from the 1960s. One of them had this competition spread where a model was wearing six different outfits and readers had to vote for their favourite. Guess who the model was? My mother-in-law!

So far, I've changed pretty much everything in the house. When I bought it, there were three bedrooms; there are only two now. I'd no real idea what I was doing, just making it up as I went along. For example, I'd initially had an idea to make one massive space for the living room and so we knocked down the connecting wall, but I didn't think it worked and so I put it back up again. Half of it is now used as a sort of home office, though lads from my real office [in nearby Portobello Road] often kip down here.

Outside, as you may have noticed, I've built a sort of high fortress around the front garden, like we've cocooned ourselves in. The reason? Well, there was a strange incident shortly after we moved in [which he declines to elucidate upon] and I didn't want that happening again, certainly not after my daughter was born [in December 2004]. I tried to do it as tastefully as possible, based largely on something I'd seen in Venice Beach, California, but I'm not sure the neighbours like it. I do, though.

The other idea behind it is that some day I'll knock out all these front kitchen windows and put French doors in to create a patio, because that's where the sun is first thing in the morning and where we'll have breakfast in the sunshine. And while we'll be able to hear all the noise from the street, we'll be removed from it, and have ourselves a little privacy.

My favourite room in the house is actually in the garden. It's like an elaborate shed, but it's another bedroom. My cousin is living in it at the moment. It's got a sink and a shower; he loves it. Everyone does. It's so cosy.

Naturally the garden was really important to me. This one was beautiful: a lawn, a pond, everything, but I've decked over it all because I didn't want my daughter running around near open water. I've put a hot tub in now and also a sauna, which is so big it had to be lowered into place by crane. For some reason, I've never plugged it in; it's never once been used. My wife hates it.

Upstairs is still very much a work in progress as well. The main bedroom is huge and bright, and I've put in a free-standing bath in front of a huge window that looks out on to the garden, which is flanked by a horse chestnut tree on one side and a willow on the other, and right down the middle you've got an unbroken view of everyone else's garden all the way to Wembley Stadium. Just here to the right is a wet room, but that was a bit of a disaster because of the rubbish builders. Every time you turn the shower on, it leaks down into the ceiling below, which has already collapsed once, and so we can't use it.

Officially, the family have moved back to Ireland now [County Wicklow], largely because my wife wanted our daughter to grow up in the countryside, but I like to think of this place as my London bolthole, a big apartment, if you like. It is frustrating that it's still so far from being finished, not least as I'm the most impatient man in the world, but I'm learning to be patient, necessarily so.

I'd never get rid of it because it really is such a nice place, and it's also gone up a lot in value. I got it for just over £250,000; it's probably around the £700,000 mark now. I bought it pretty much on instinct, so I guess you could say I have good instinct. The house in Ireland I bought on instinct as well. My wife never even saw it beforehand. Does she like it? She's slowly coming round to it...

Diarmuid Gavin, 43, is a TV gardener who has hosted several shows, among them Gardeners' World and Home Front. He has won many awards, including a silvergilt medal at this year's Chelsea Flower Show. Raised in Dublin, he lives in Co Wicklow, Ireland, and also in this house in north-west London. His latest book is co-authored with Sir Terence Conran.