There’s always been an affiliation between flags and festivals. Glastonbury’s always had lots of flags up in their viewing areas. It looks beautiful so this may explain where the idea originated from.
However, since the BBC got broadcasting rights for Glasto, many people now make enormous flags just so they can see themselves on TV. It’s got progressively worse and is only really a problem in the main area in front of the Pyramid and Other stage (unfortunately this is where the cameras are, so this is where the flags are too!).
It got so out of hand that there was a vote on the Glasto website this year as to whether or not flags should be banned outright. Most people don’t want that, the flags are part of the fun and the beauty of Glasto. I voted no, and so did most people, so no ban, but it’s clear that something needs to be done so that flags aren’t blocking everyone’s view. Emily Eavis says, "No ban, but the front of the arenas will be kept flag free". I imagine no flags will be sold on site, and people with huge flags will not be allowed to take them into the centre of the main arenas. Good job, because things have got worse year by year.