Everyone knows you're passionate about all things historical, but what was it about this show in particular that excited you?
I suppose as you get older, what's happened before us on the Earth tends to get nearer. When I was a little kid, the Second World War seemed ages away, yet I was born in 1946. So it was about nine months before I was born. As I grew older, I realised the Second World War was near me because my grandfather was still alive and he'd fought in it.
Gradually, the older I got, the more the Georgians seemed very modern, the Tudors seemed very modern and the Romans coming here seemed very modern. Then, about 10 years ago, I realised how close to us the Bronze Age actually was. And then how close the period was when the North Sea was inundated and Britain was cut off from Europe.
Twenty years ago that would have seemed so ancient that it was beyond conception. Now, even the moment when human beings took their first tentative steps towards Great Britain seems part of something I can get my head around. So, I wanted to look at something that had happened before that.
That's a long way back even by your standards - did you know much about that period already?
How much do I know about anything? I'm one of nature's great generalists; I know bits and bobs about everything, then the few bits of information I have I test out with people who know things... and discover I didn't know much at all! Then I start to build up a narrative about what's really happening - you have to reinvent your whole mindset.
Did you feel out of your historical comfort zone?
Rather than taking me out of it, it was stretching it by taking me further and further back. I wanted to test my mindset on geology and geomorphology as they are things I'm constantly confronted by.
I've always been aware of the drama of the British environment because I was of the generation who spent their summer holidays in Britain - culturally, that was just what you did.
As a child I was aware of the Lake District, Scotland, Devon and Cornwall in a way that huge numbers of children aren't these days. That will be one of the few positive aspects of the recession: many people will holiday in their own environments. That's not a bad thing.
Going back to those places of my childhood and learning what created them was not only very dramatic for me, but in an odd way true of where we're going to be in Britain over the next few years - reassessing what we have ourselves rather than marvelling at the Grand Canyon or the Pyrenees.
You visited some of the UK's most spectacular places; does that still excite you in spite of all the travelling you do for work?
It couldn't fail to excite me. One of the geologists on the show said there is a greater variety of geology in Britain than almost anywhere in the whole world - it's a funfair of archaeology.
Much of the filming was done in the depths of winter, and god knows I've had enough of that in the last few years. It was often difficult, but it was never less than inspiring. I never thought, 'Sod this, I want to go home.'
Not even after climbing your third mountain of the day?
The amount of walking and climbing was pretty unusual, but the secret with television is to get as close to a main road as possible... and then make the background scenery look as wild as possible!
We were up at dawn and carrying a lot of heavy equipment around, but it really paid off and created a really good team spirit among us.
You visited Hornchurch to see evidence of the southern-most point of Britain's ice sheet, and admitted that although you grew up not far from there, you had no idea of the history that was on your doorstep. Do you think that's true of most people?
I'm absolutely sure it is. I know that because of the conversations I've had with not just kids but adults, who have been confronted by these great prehistoric dramas, but were totally unaware of them beforehand. They didn't realise the significance of where they lived.
Have you noticed any improvement in that since you started making these kinds of shows?
We know there's been an improvement in people's perception since we started doing Time Team, and that is one of the things in my life that I'm most proud of: that, even in the most rudimentary way, people understand what archaeology is, how it works and why it's valuable. Whether that's also true of our geology, I don't know.
What did you enjoy most about making Birth of Britain?
The most fun thing was panning for gold in Scotland - and actually finding some! It genuinely wasn't just done with the magic of television. I was very excited. The tiny piece I found certainly wasn't going to buy me a Porsche though.
But you kept it?
I lost it! I put it into a plastic bag and it was just so small that it must have fallen through the molecules that made up the bag. It didn't even make it home with me. I think I'd lost it by the time we passed Carlisle.
