New apple tree

[Dirkdigger]

Help, I'm thinking of buying an apple tree for my plot. The variety I'm hoping to get is Beauty of Bath. It says it needs other trees to pollenate. How far away would be acceptable, for the other trees. Its just a man a couple of allotments along has lots of different apple and crab apple trees. Any advice would be appreciated.
I will try and pick his brains when I see him, but before then please, please help.

[Dirkdigger]