Tom, I've played in a load of nursing homes over the years. (I'm in Ayr, so not far from you)
It's best if you do songs they know, simple ones with a chorus (Coulter's Candy, the Red Yo-Yo) that type of thing.
And one great thing I learned about elderly people.....Don't be surprised if you get minimal applause, they vote with their feet. If you still have an audience at the end of your set then they enjoyed it!...Good luck