I can't quite work out how many people would be allowed in though:
"
Some large events, including conferences, theatre and concert
performances and sports events. Controlled indoor events of up to 1,000
people or 50% of a venue’s capacity, whichever is lower, will be permitted, as will
outdoor events with a capacity of either 50% or 4,000 people, whichever is lower.
The Government will also make a special provision for large, outdoor, seated
venues where crowds can be safely distributed, allowing up to 10,000 people or
25% of total seated capacity, whichever is lower. In addition, pilots will run as part
of the Events Research Programme to examine how such events can take place
without the need for social distancing using other mitigations such as testing"
So if HJ holds 15000, which perhaps is 6000 seated, 9000 standing (at a guess) does that mean it'll be initially capped to 1500 (6000 * 25%) ?
But that'd be the same as if your stadium just comprised of capacity 6000 all seated.
So I guess there might be a different calcution where a stadium comprises of mixed standing & seating - which would fall into the upto 4000, but no greater than 50% capacity, limit (and perhaps that would mean 1500 seated, 2500 standing ?)