Hi S - get on to the nice people at Brogdale and they should be able to help - you can send them a picture of the tree - include the leaves and the fruit etc, and see if they have anything similar / know the variety.
http://www.brogdale.org.uk/
There are 2500 varities in the UK plus apples can 'interbreed' so you may even be eating a unique fruit...thats how Bramleys came about....
And come along to Edinburgh Farmers' Market on Saturday (Castle Terrace, 9 - 2) - we have a Guinness World Record attempt at making the worlds' biggest bowl of porridge..........and you can get loads of good fresh seasonal stuff too of course....including a nice bag of freshly cooked real potato crisps from The Crisp Hut..