BMW M6

The BMW M6 might be convertible, but the people who drive it are unlikely to be

Would suit: Louis Theroux (bought with my royalties)
Price: £87,365
Performance: mph 0-62mph in 4.8 secs
Combined fuel consumption: 18.6mpg
Further information: 0800 325 600

It is now two years since I published my first proper book. After the initial sales flurry – caused almost entirely by members of my immediate family, who felt they ought to check in case they had been libelled in some way and might make a few quid – I see from my hourly checks on Amazon that it is currently "bubbling under", as Alan "Fluff" Freeman used to say, at around the 250,000th mark. This means that around a quarter of a million titles are selling more than Just as Well I'm Leaving (*). Which is off-putting, not least in view of the imminent launch of my next book, Sacre Cordon Bleu (**).

I blame the "customers who bought this item also bought..." function on Amazon. Right now the customers who bought my book also bought one by Louis Theroux, which is bound to be funnier. Even I can see that. Anyone thinking of buying my book is going to head straight for Theroux's mighty canon. I know I would.

What if this information were available to car buyers? Just as you had made up your mind to buy a new Fiesta, up would pop a message telling you other buyers went on to buy a Suzuki Swift for two grand less. "Oh," you'd say to yourself. "I hadn't thought of that. Two thou less, you say? Hmmm." Ford would soon run out of beleaguered European subsidiaries to sell, and then what would it do?

But what might BMW M6 convertible buyers be tempted by? Unlike super minis, which are as common as starlings, £90k four-seat convertibles are few and far between. The Aston Martin DB9 Volante is £30k more expensive, and the Bentley Continental around £50k more. The Porsche 911 convertible is a closer rival, although that starts at £68k and it is a very different kind of car – much smaller, sportier, more focused. As for the Jaguar XKR, that was obsolete before it was launched: why not buy your wife a spinning jenny while you're at it?

Certainly none of the above have the M6's clunking fist of a 500bhp V10 engine – essentially, an F1 unit with slightly longer service intervals – mated to a super-alert, seven-speed sequential manual gearbox which you can operate either with the lever or wheel-mounted paddles, or just stick it in auto and use your left foot. None except for the M6 coupé, of course. They are, after all, the same car, except that one can lose its roof in 22 seconds. That said, the convertible is 20 per cent heavier than the coupé thanks to that old soft-top bugbear, extra chassis strengthening. It carries it well, though. Even though the convertible has a softer ride, it controls roll on corners and, according to BMW, the acceleration is unaffected. But overall it does feel slightly slushier than the coupé and, with the roof up, it is less easy to see out of. So the question then becomes, is it worth £5,000 more to hear the glorious bark of that incredible engine that bit more clearly? The answer? Of course it is.

So what, then, would M6 customers also buy? Well, a matching coupé, obviously.

(*) Please buy it: you don't have to read it. (**) Actually, buy this instead – it'll be better, honest.

It's a classic: BMW 328

Like the M6, the BMW 328 of the 1930s was the company's flagship convertible sports car. But that is where the similarities end.

The 328, designed by Fritz Fiedler, was BMW's first sports car. It was incredibly advanced for its time, with alloy body panels, hemispherical combustion chambers and a tubular space frame chassis. Though it had only 80bhp, its lightweight materials meant it was fast and agile and its sleek styling was hugely influential, not least on the Jaguar XK120, which couldn't match the BMW for racing success – its ultimate achievement being winning the Mille Miglia in 1940 at a record average speed of 104.2mph.

After the Second World War, the 328 continued to be made in the UK as a Bristol 400. Its influence continues with a recent BMW styling project, the Z4-based Concept Mille Miglia, unveiled last year.