You're looking for something like Farecla G3/G5/G6/G10 rubbing compound. Like all abrasives, the higher the number, the finer the finish. There are lots of other similar products; what you buy will depend on what you can find like locally. A look in your Yellow Pages will lead you to an automotive paint supplier who will be able to help you with what you need. That will include which polishing head to use with each product.
You can buy this stuff in Halfords, but a trade supplier will be much cheaper.
A polisher will easily polish or burn through paint if you're not careful especially on edges. Some practice on a panel that isn't important would be a very good idea! G3 used by hand will refresh badly oxidised paint, but it is a lot of work. The polisher is used to speed up the process and reduce the effort involved.
These products are not polishes; they're to create a finish ready for polish which you will have to apply afterwards.