The plan was to make a claim under the UK version of 261. However after reading the forum and some other horror stories about claiming against Vueling, I’m thinking it may be better to go against BA directly.

Horror stories - https://www.theguardian.com/money/20...refund-request

it looks like Vueling refuse to accept delivery to the Gatwick address. That said, there appears to be a trick whereby a claimant can post the claim from 2 separate post offices with a certificate of posting, but not recorded. The issue with recorded, is that Vueling refuse to sign for the delivery.