Difficult one

For the proper old ones you need something from the voice of the people and for the rest something like the "acoustic folk box" or one of the many topic samplers called "the folk collection". I've had a quick scan through my "various artist" section on the CD shelves and can't find anything thta fits the bill in both areas so I'd suggest expanding to two CDs

go for The Voice of the People sampler Topic TSCD751 and the Voice of Folk Topic TSCD705 I think they are both reasonably mid priced to stretch to two CDs.

Of course you'll get a bit of Scottish and Irish (and quickly checking, Welsh) in there as well but borders are there to be crossed.