An individual who attends parties, openings, social gatherings and events with the sole intention of obtaining free food and drink - an arch blagger.
A similar definition can be found in Wiktionary:
ligger (plural liggers)
(slang) A freeloader or hanger-on, especially in the music industry.
Peaches Geldof may be a top showbiz ligger – but now she’s got a group of her own. – "Peaches gets own band", The Sun, 29 Aug 2006
The ligger caused a scene when he begged one reveller to find him some gear – and offered sexual favours in return. – "Wicked Whispers", The Mirror, 29 Jan 2005
That is, ligger is apparently British slang for a mooch or freeloader, originally or especially in the music scene.
But while this sense is attested in crowdsourced dictionaries (which lends credibility to its status and usage as slang), I can't seem to find it in any dictionary produced by professional lexicographers (which probably means it's relatively new or relatively unpopular slang). Etymonline comes up dry, too.
In fact, the only clue towards etymology is from the same UD definition:
Popularised by the NME in the early nineties and possibly with it's entomological¹ roots in the fishing term for "baited line".
The NME is a popular music rag (h/t @Josh61), and while a baited line seems metaphorically apt, and ligger is indeed recorded in professional dictionaries as meaning "baited line", I'm left a bit skeptical because (a) I don't see a lot of opportunity for cross-pollination between anglers and scene kids, and (b) the ligger is the baited line, but liggers are those who pursue the bait. So there is a whiff of folk etymology here.
What are the origins of this freeloading sense of ligger? How widespread is it? Does it still have currency?
¹ I know what you're thinking, but no, there are no bugs in this question's title. We're talking about liggers, not chiggers.