I guess the covid rules would have them seated and masked , one way systems and the like, which probably for Bryan Adams wasn't feasible. Though outdoors seated there is minimal risk I would have thought and masks would make the whole thing rather joyless.
Fill yer boots on the guidance...
www.gov.uk/government/publications/coronavirus-covid-19-organised-events-guidance-for-local-authorities/coronavirus-covid-19-organised-events-guidance-for-local-authorities
All events recommencing at Step 3 will be subject to the following capacity caps:
1,000 people or 50% of a venue’s capacity, whichever is lower at indoor events
4,000 people or 50% of a site or venue’s capacity, whichever is lower at outdoor events
The government has also made a special provision for large, outdoor seated venues where crowds can be safely distributed around the venue, allowing up to 10,000 people or 25% of total seated capacity, whichever is lower. This provision can be used by venues with a seated capacity of 16,000 or above. For events with mixed seating and standing areas including music, elite sporting events and non-elite/professional spectator events, the capacity cap will be calculated as 25% of seated capacity, irrespective of any standing capacity. All spectators admitted under this provision must be seated and should not access the venue’s standing capacity to view the event. Where the crowds cannot be seated at a large outdoor venue for the duration of the event or the seated capacity does not exceed 16,000 the cap of 50% of the site’s capacity up to a maximum of 4,000 people will apply.
All capacity restrictions must be adhered to at any point throughout the event. For example, a theatre can admit over 1,000 people in a single day, but no more than 1,000 people at one time. If an event runs over the course of multiple days, no more than 1,000 people should be admitted at any one time over that period. If a single venue hosts multiple different events at one time, and the attendees of each event are separated for the duration of the event (for example, a cinema with multiple screens, or an exhibition centre hosting multiple business events), the 50% capacity cap will apply to each individual event, rather than the venue.
This should be applied consistently across all types of events apart from grassroots organised sports participants events which are not subject to the limits on participants, but they are still subject to limits on spectators.