I reckon they’ll take it 1:1 if it’s in Euros. Somehow you’ll be able to use it. Is your flight outwith the UK?

I’m going to stop buying these vouchers after my experience on BRS-EDI a couple of weeks ago. If the flight block time is longer than 1h30 and it takes place over a mealtime, then I will take it….if it is offered. In fairness, the easyJet BoB menu is really quite good these days and not too expensive. It can really offer a good deal if leaving from Swiss airports.