a right old Cockney knees up

Scrolling through the Aladdin’s Cave of curiosities and strange delights that is eMusic’s soundtracks/ other section; I came across this collection of British Pub Songs. They’re not presented in the best way here – far too much evidence of electronic input and bad production for songs best sung whilst having ‘a bit of a knees up round the old Joanna, with a pint of porter in one hand and the better half in the other*.’
What really surprised me is that I know nearly all of the words to 14 of the featured songs and I have no idea how. In the pubs I visit, if spontaneous singing happens at all, it would probably be a few bars of Rihanna or Oasis (or if I’ve timed it really badly and the football’s on, something along the lines of “Go on Arsenal! Goooo on Arsenal!” “Chelsea are a load of w*nkers!”) The songs on ‘British Pub Songs’ belong to a bygone age of Blitz Spirit and the Kray Twins. So why am I sitting here singing ‘Bye Bye Blackbird?’
I’ll discount the sinister idea that something ‘they’ put in tea bags imparts knowledge of ‘My Old Man’s A Dustman,’ meaning it has to be some kind of collective consciousness: evidence of a genuine folk tradition, passed down and around through grandmothers’ singing and archive TV clips. Can anyone enlighten me as to what the equivalent versions in other countries would be?

*Translate Text – Old Fashioned Cockney to Standard English:
‘a small party surrounding the old piano, with a pint glass filled with dark-coloured beer in one hand and your spouse or partner (usually female) holding the other.’