Why not do what we used to do, namely, take some clothes you are content to dispose of and after wearing them, then dispose of them!
I imagine a left luggage facility for the folk riding LEL might be something the organisers might wish to leave to entrants to sort. Although the last PBP did have one that I used, slightly larger organisation.
Get to the local charity shop and choose an outfit that can be donated to others after your Saturday night in London.