One day, there won't be any cars. I suppose a few will linger on in museums and in the hands of bloody-minded enthusiasts, but no one else will give a pig's ar*e.We'll have come up with something better, and why not? It's happened before, after all. Every month, I sit here with my pencil in my gob thinking up new things to write in this top-ranking website on the subject of cars and driving. I also help present TopGear TV, a globally consumed sitcom themed around cars, but for the entertainment of normal folk who often aren't actually interested in cars at all. But it's sort of relevant nonetheless, because everybody uses cars in some way.You will notice, though, that there is no equivalently successful magazine or TV show about horses. Or canal boats, or driving traction engines. These are the stuff of transport history, and, eventually, the car will join them.So, the Hayneses and Lord Montagues of this world, the preservers of our car heritage. What should they be buying up for the bafflement of a generation as yet unborn? All sorts of things, I suppose. Small cars, exotics, the Nissan Leaf. They're all part of the story.But what about the investors, the bankers with their bonuses, and everyone who has recognised that a pension or a Post Office savings account is a waste of time? Buy rare and interesting old cars, the theory goes, because they're a safe place to put your savings and better than money in the bank. But I think that, long-term, they're making a mistake. When no one cares about cars any more, these things will be worthless. The only car worth investing in is - bear with me on this - the Reliant Robin.Now. I don't like to boast, but I think it's fair to say that I am a world authority on the game of car football. We've played it on the telly, in Toyota Aygos, but mainly we play it as part of TopGear Live, when we use our away strip. Which is the Reliant Robin. I may have played 100 games of car football in Reliant Robins.The Robin is the ideal car football car, because it falls over. This is amusing. You can take a dive in Reliant Robin car football simply by yanking on the wheel. The crowd loves it. Small boys and girls jump up and down on their seats and wet themselves with excitement as another Robin goes down and the giant comedy football flies into the crowd.But the ease with which a Robin can be flipped onto its side is also a tactical tool. I have saved deadly shots with a lurid last-second slide across the goalmouth, and, in a recent match, I saw our team achieve something that the real England never has\: a winning goal from a quick one-two and a diving header.There is, in fact, an offside rule in Robin car football, which is that if you're going to turn it over, fall onto the offside, the driver's door. Otherwise you half fall out of the seat and the harness digs into your plums.The thing is, every year we reinvent the TopGear Live stage show with new acts and stunts, but we often just put Reliant Robin car football back in at the end, as usual. And why not? Real football has been going on for hundreds of years and millions of games, and it hasn't become boring yet. Car football is still football, so it's always good to watch and full of delicious uncertainty. The only predictable aspect of it is that a lot of Robins will fall over.So I started thinking the other day during a game in Australia, as I lay on my side waiting to be righted again\: why isn't Reliant Robin car football an international sport? Firstly, it fulfils mine and Jeremy's requirements of a sport, which is that it should be a competitive game but not involve any physical effort. The exertion demanded by it extends only to driving around a bit.More to the point, Reliant Robin car football is great fun to play and very exciting to watch. It would be even more exciting if there were national and international championships and, ultimately, a World Cup. These, in turn, would generate a Sunday league sponsored by something like a paint manufacturer, and car football in schools.I don't see why this shouldn't happen. In fact, I can't imagine why it won't happen eventually. In which case, we're going to need a lot of Robins. We may even have to start making them again. Robins are going to become valuable. Cashed in your ISA? Downsized to a smaller house? Sell Italian exotics, and buy Reliants. And that's a TopGear Top Financial Tip.