Now is there anything that I would be expected to bring, say, etc.
It will be nice if you bring presents for the whole family. They should be just symbolic, so don't worry too much. Treat it as a sign that you remembered about all the family members (even the ones you're seeing for the first time). It's just appropriate to give a little something to every person present at a Christmas Eve, so I'd advise you to ask your friends who's invited.
Expensive presents are bought only to the closest ones (like spouses, parents, children), so you're not included in 'serious' present exchange. If there's a kid in the family - the present for the kid may be slightly more effective than for the rest.
Have them packed and tagged with you, and just put it under the Christmas Tree before the Eve starts.
And is there anything that I might do as a Scotsman, without thinking, that would cause great offence to his family...
Always be happy about the food (warning: carp is very... specific).
Dress formal (in most families a suit and a tie would be OK).
When the dishes are served, take only a little of each (watch how much the others take). According to the tradition, one should try all of the dishes and you can expect around 12, so be careful to have some 'room' for the ones that aren't on the table yet.
When all the dishes have been brought in, you can decide of which to take more (but remember about the desert!)
And don't worry, be relaxed. If you realize you've done something wrong, just apologize and smile.