There are forum users much more knowledgeable about that subject that I am. But in short, some watch manufacturers make their own movements in house, Seiko for instance, but many more buy them from movement manufacturers, most notably ETA.
Wow - £8 is a good price to pay! Well done.
If it's running intermittently at the moment - and you only paid that much for it - I can't see anything wrong with having a bash!
The advice from many of us here would be: As you go along, take notes/photographs of what you do so you can reconstruct the movement after disassembly.
Sounds like it needs a good clean. Best of luck!