the dates upon which I've heard and sung this version of Knees-Up have been countless over the years; from at least 1950 onwards (probably my first exposure to it), and in all situations since from weddings, wakes, pubs, impromptu parties and, on occasion, although the environment would obviously preclude any active participation, with the exception of the odd joyful individual, on board the bus on a day trip to the seaside or wherever, usually on the return ride home. (Always a good feature of day outings on the bus in the UK -- a good old sing-song on the way home.)
As a sidebar, the song is commonly introduced, not by its title at all but by simply saying to the audience something to the effect of "Let's 'ave a good old knees-up then!" They all know what's coming. Equally as often, without any prompting, a knees-up will suddenly self-generate and blossom throughout the crowd in seconds.