The venues that I recognise on this list, including the Camden Underworld which I believe is the largest at 500 cap, do not require the NHS Covid Pass (double vax, recent infection and recovery or negative test within last 48 hours) - there are also no Scottish or Welsh dates (covid passes required by law in these countries, in Scotland there is no provision for negative tests, unvaccinated people are completely excluded from large events) which suggests this is an intentional choice to have as few covid related barriers to entry as possible.