Two questions about this song.

Fistly, I have a distinct memory of hearing the song sung with the couplet "Making love to Hannah in a big armchair, is like walking through Alaska in your underwear", instead of "An evening spent with Hannah sittin' on your knees, Is like drivin' through Alaska in your BVDs".

I can't remember who sang it, it may have been George Melly (a multi-talented British jazz singer ) but then again it may not. If it was in fact George Melly did he change the lyric to make it more comprehensible to a British audience, or was his the original lyric and did Ella tone it down as being slightly too raunchy ?

Which brings me to my second question. I know that BVDs means underwear, but why are they called BVDs ?