The wikipedia article indicates that different subspecies of Viscum album are fussy about their host tree, but that you will find in UK is likely all V.album subsp album which appears to be rather catholic about its host, though it is rarely found on oak and never on conifers; other subspecies specialise in these but are not found in UK.

This page from Kew has some notes on their attempts to grow it, and it does not appear to be host specific, they got seed from one collection to grow on diverse hosts, though with a lot of failures. They seem not to have tried the birdpoo trick, and did not think nicking the bark was necessary. They note that light is essential to germination, so the birdpoo should be around but not covering the seed, and don't do the covering with moss I suggested.
Plants & Fungi: Viscum album (mistletoe) - Species profile from Kew
Sounds like I was quite lucky given their success rate.