Wow I seem to have spurned some debate here. Thanks for all the contributions.

It is my (very uninformed) opinion that 5/4 is actually a rather natural rhythm to sing in English, especially the 1-2 1-2-3 form of it. The songs I know in 5/4 (Bold Fisherman, Mariners All, There Was a Young Farmer) all lump along in such a natural way that I wouldn't be at all surprised if the rhythm had formed a greater part in the English tradition and some of these rhythms may have been bent into 6/8 or 4/4 to suit the prejudices/narrow music horizons of some of the collectors.

Keep playing those tunes

-cjc