Reminder the UK is no longer member of the EU.
Therefore EU Citizens will need a passport and ETA to enter UK, e.g. for the Cambridge Interop.
From the 2nd April 2025 UK requires a ETA fee of £10 for non-UK person.
I can be paid by an app.
All details here:https://www.gov.uk/guidance/apply-for-an-electronic-travel-authorisation-eta