Upvote:4
There are two things you can definitely do:
So if you do get a UK visa in your current passport, you will in any case be able to travel with that visa and another passport after the first one expires.
I don't know exactly what will happen to the current visa application (e.g. whether you could put the visa in a new passport even though you submitted your old passport's number) but I would keep the old passport in any case.