Thanks again for your help Martin. However, there is a new problem!!! As you know, last night, I tried touching what I thought you meant by the contacts, (but I see from your new post it wan't the right area). So, as I was getting a bit frustrated last night, I gave up on fiddling around with the cartridge. This morning, I decided to listen to the radio for a while. But now I am sad to say, the radio doesn't work either! I'm sure it can't be anything serious because it was working perfectly yesterday before I started messing around with the cartridge.
Anyway, back to the cartridge - I think that I have proved there is a fault with it by another means. I also have a 2nd B&O - a Beocenter 5000 - that has been sitting in the cupboard under the stairs. I dug it out this morning and tried the stylus in it. The result was the same as in the 7002 - sound from one side only. I assume this proves the stylus is faulty?
As regards the radio, can you make any suggestions as to what I might have done to stop it from working? I hope I am not being too much of a pest!