You've just published your third motorway sightseeing guide. How did it all begin?

I was a location director on the BBC's Antiques Roadshow, making the little opening scene-setting films. I live in Worcestershire in the Malvern Hills and the Roadshow is based in Bristol, so I was driving up and down the M5 almost every day. In fact I used to drive along motorways all over the country, often with Michael Aspel, and we would see lots of interesting buildings along the carriageway. I got the idea to write a book on the M5. It worked very well, so I followed it up with guides to the M6 and then the M4.

It seems an odd subject for a guide book

It's fascinating because it is an arbitrary exploration of a slice of British countryside. The determinant for the book is: can you see the structure from the motorway carriageway? If you can, it's in there. The M4 book runs west to east, so it starts just north of Swansea and runs to Chiswick. We try to avoid replicating what is in the general tourist literature and I got a lot of stick over Lichfield. Everyone expects the city's cathedral to be mentioned, but instead we mention the Co-op headquarters.

How do you expect people to use the book?

We are at pains on the cover to make clear that the book shouldn't be used while driving. It is best enjoyed before or after your journey. I'm just hoping to make people's journeys more pleasurable and enlightening.

Can you learn much about a place by speeding through it on a motorway?

You could go from Swansea to Chiswick and not have any sense of a change in culture if you stick in the middle lane. In fact, if you visit every town and city along the M6 or M4, as I have done, you become sorely aware just how many chain stores constitute high streets and how similar they are even 200 miles apart. We are losing our diversity. Except in Wales where they have maintained lots of small businesses in their high streets.

However, there is plenty of interesting local culture and the purpose of my books is to offer people making that relentless, long, utilitarian journey a flavour of the bit of country they're passing, whether it is by telling them about the supermarket depot or just a little bit of anecdotal stuff about what one of the farmers told us. Suddenly that stretch has gone from dull anonymity to having a bit of character.

You must be a big fan of driving holidays

I've had to drive all over the UK as a director, but the green bit of me thinks that we're all doing too much driving. In the M4 book I've suggested people actually go by National Express coach or even by train. I hope I'm not encouraging motoring per se.

Which is your favourite part of the M4?

The bridge over the Severn is fantastic. There is a small visitors' centre in an old Portakabin that was one of the contractor's buildings. If you pop in you get a real sense of the amazing civil engineering of those two bridges and they're always a delight to drive over.

The other part I like is the first mile or so west of Chiswick, which is just fantastic. It sits up above the Great West Road. When I was doing the research I walked underneath the M4, taking photographs of all the buildings you can see there and there's a real density and richness of contemporary commerce. I hope that commuters who bemoan that journey will now see it in something of a different light.

· The M4 Sights Guide is published on 16 July by Severnpix Publishing, £9.99, www.severnpix.co.uk.