Life, the Universe, and Returned Payments
I've just received £42 in returned refunds from PayPal - about two thirds was from people who it turns out don't currently have PayPal accounts set up for the email addresses they'd given me, the rest were people who declined the refund, one of which was my error, a person who'd already said he wanted his money to go to charity. Since I have no good way to chase up the others, all of this money will be donated to Cancer Research UK.
Update - paid to Cancer Research UK 6th July 2016. New total for that charity £2342.
If anyone thinks that they should have received a refund please contact me, otherwise I hope that this process is now complete.