The retailer I am buying my carpet from has offered to treat it with a protector – I think with Scotchgard, or something similar. It is quite expensive, but is it worth doing? And is it safe on wool carpets?

Protectors, provided they are WoolSafe approved (ask the retailer if it is approved!), will not cause any damage and will show an improvement in resistance to soiling and staining, especially on a light-coloured carpet. Spots are also easier to clean.

Please remember, though, that these treatments are never quitefull-proof: when you have a spillage you still need to mop it up as soon as possible. If you leave it a stain may still develop.