I think some pubs do switch to plastic during times of high spirits (pardon the pun) like during football matches or carnivals to prevent injuries caused by either throwing glass or broken glass on the street. Not sure if this is required by law or whether it's something that is just done.
Just did a spot of searching, what it seems to be is that periodically (every couple of years or so) someone from a University or a think-tank will say that pubs should serve alcohol in plastic glasses and bottles to prevent people hurting themselves, the BBC will run an article on it, the Wine and Spirit Trade Association will protest the 'blanketness' of it and then it'll be forgotten about for the next two years.
Turns out there was a new one just five days ago!
http://www.bbc.co.uk/news/health-11392685