Party Time in London

I was out and about in Covent Garden Friday night, when I came across this party of South Wales lasses, all set to have a good time for "Leanne's Hen Weekend". It was early, and none looked worse for wear yet, but I suspect that might not have been the case later. I wonder, is the over-the-top party a uniquely British thing? I can't say I've noticed it in other countries (except with Brits travelling overseas for the occasion).