I've just been given my first car - a 1998 Ford Fiesta non-turbo diesel. I'm the fifth owner. My dad says that I should always stick the best fuel possible in my car because, having done 200K miles, it needs all the help that it can get, so I've always used Shell V-Power Diesel.

But my uncle says that, for the very same reason, I may as well use cheaper supermarket fuel: my car is so worn and old that a premium fuel won't make any difference. I remember you saying once in the newspaper that premium fuels help protect the engine parts better?

Whose advice should I follow? My dad's or my uncle's?