IMHO that sounds like the BB axle is too short.
Well yes, I did check the chainline this morning and it was a bit short (47mm) with the new chainset fitted, so I replaced the bottom bracket and managed to increase it to 50mm as specified for the Inbred frame.
However the Tourney, which now I come to think about it, came off a hybrid bike with a 73mm BB shell and a long axled BB, continued to hit the bottle cage. Having checked the tech docs for the Deore LX it would appear that it is 48t compatible but has a 12t
minimum capacity between top and middle rings. This explains why setting the height of the fd correctly WRT the outer ring was causing the inner plate of the fd cage to foul the middle ring.
I've now set the height so that the inner plate just clears the middle ring and along with the new BB, things seem to have improved. I'll take it for a test ride tomorrow to see how it works in practice.