Based on that list, depending on whether or not they rounded a lot when reporting the 500 bed figure, it comes down to 3 hospitals that would be the logical first step to checking. Chase Farm Hospital technically has 509, Northwick Park Hospital has "~500," and Homerton University Hospital is reported to have exactly 500 on the Wiki, but their About Us section says "almost 500."
Maybe they have a secondary sight with like only 5 beds for rare quarantine cases? Otherwise, rounding must be no issue for a mere PR, which would open up more potential candidates to check on.