Our bee group was alerted to a swarm in Golden Cross square right in the heart of Oxford yesterday. The swarm had mustered under an umbrella at eye level. We scrambled to find somebody to collect but someone from outside our group attended before we could get organised.
Where there are swarms there should be colonies nearby. To have a swarm within metres of Carfax Tower (the 'centre' of Oxford) suggests roof-top hives since the nearest garden is a few hundred metres away (Jesus College; Christ Church College; Lincoln College; St Peter's College). It is possible that there are ground level hives but it would be harder to place them where they wouldn't be a nuisance to people.