Reading further into the UK regulations.
"Tickets for safe standing in seated areas should comply with the recommendations on information and design outlined in Section 3.30.f of the Green Guide.Under no circumstances should there be any sale of unreserved places for areas of safe standing in seated areas"
"Ticket holders are required to occupy the space in front of the seat allocated to them on the ticket – that is they cannot migrate to different spaces within the section, as would be possible on conventional terraced standing accommodation"
"Ticket holders will not be permitted to admit non-ticket holders to the section"
"In order to prevent non-ticket holders from entering, it will be necessary for management to place stewards at each entry point to any seated area used for safe standing."