Question VAT Refund Process When Leaving UK with EU Purchases?

[TrailBlazingBecca]

I'm planning a bus tour that starts in London, goes through Europe, and then returns to the UK. I'm curious about the VAT refund process for purchases made in the EU when leaving from a UK airport. Does anyone have experience with this? Specifically, how does it work when your trip starts and ends in the UK but includes EU countries? Any tips or things to watch out for would be really helpful.