Dot - re your bay trees. I keep mine in a sheltered corner of the terrace over winter - if we're going to get a very hard frost I bubblewrap the pot, but it's survived over 10 years outside since I grew it from a cutting.
The thing that kills bays is cold coupled with wet roots, so keep the pots fairly dry and they'll cope with quite a lot of cold. As you live up there in North East Scotland where it can get very hard, I think I'd put them in the greenhouse when the weather gets very bad, but make sure it's well ventilated.
I wouldn't put them indoors in your house - they'll get much too warm and start into soft growth which you don't want.
As I said, keep the roots fairly dry in the winter - raising the pots on bricks or little pot feet will help to keep them well drained. In summer they need more water, but again, they don't like soggy bottoms 