Kate Humble: 'It was exciting being in a big city at 19, living on crisps, air and drugs'

I spent my whole childhood covered in the dung of various animals I grew up in a house next door to a farm in Bray, Berkshire. Most days I'd climb over the fence into our neighbour's farm and muck out the horses or the pigs.

British wildlife is just as exciting as the animals found in Africa OK, we might not have big cats with big teeth here, but we've still got astonishing animals, from hedgehogs to basking sharks. What's so important about Springwatch, which I presented since it began, six years ago, until last year, is that it inspires so many people to notice the wildlife around them.

For an island nation, we don't have a proper connection to the sea The British public doesn't care about what's going on in our coastal waters because they feel so inhospitable. We might go for a swim on a July day, should we be feeling brave. But this disconnection means that most people don't think of the sea as a wildlife habitat. Yet it's the most diverse environment we have and it needs to be protected.

We are not designed to be in water I didn't realise that until I went swimming off the west coast of Scotland, to film basking sharks. They're magnificent 7m-long beasts with a huge triangular fin like a proper "Jaws". And when one came out of the gloom and straight towards me at speed, its mouth open, all I could think was: will it know I'm not plankton?

I don't miss living in London It was exciting living in a big city when I was 19, based in a squat and living on crisps, air and illegal drugs. But as I got older I realised I was knackered all the time. Once my TV career started, I'd go away filming to places such as Africa, but at the end of the trip I wouldn't want to come home back to Chiswick, which was a terrible thing to admit.

Now when I'm driving home after a trip away, I look at the fields and countryside and my heart lifts I relocated to the Wye Valley in Wales with my husband in 2007 and we now live in a farmhouse with four acres of land.

I was never interested in having kids There are far too many people in the world already. Yet there's still a deep suspicion in society that a woman should say, "You know what, I never wanted them." So I have to put up with journalists asking why I haven't yet had children. Well, how do you know that I haven't had some sort of dreadful tragedy and I can't have them?

People need to have muddy fingernails Muck is good, and without a bit of dirt, our immune systems become inert – well, that's my theory based on a small study of one: I'm pretty mucky most of the time and I'm pretty healthy. I'm sure, too, that we'd all be a lot healthier without that ridiculous antibacterial hand-gel stuff.

Kate Humble, 44, is a TV presenter and runs a Welsh smallholding in Monmouth. 'Humble by Nature' (£16.99, Headline) is out Thursday (humblebynature.com)