I share my home with 3 other people. I have received a request from a 21-year-old volunteer doctor who will work at the local hospital for 3 weeks. Should I cancel/reject the booking?
I'm not sure how this volunteer 'doctor' was able to make a booking request with you through the https://www.airbnb.co.uk/d/medicalstaysuk scheme. As you know it's only open to hosts with whole listings in the UK; as it is too high a safety risk to have a frontline worker sharing amenities with hosts, particularly in a situation like yours where you have multiple housemates.
Are you registered on this scheme with Airbnb?
STRs are illegal in the UK until the 4th July and before then only those with whole listings can accept bookings from key workers, those attending funerals and those without a permanent home.
I would give Airbnb a call and ask them how a person under the UK health worker scheme was able to make a request to you to book in a shared home set up?
Be great to hear what they say.