A material change of use is a planning matter not building control. However Building Regulations have different requirements for different uses.
The important distinction is whether a change affects compliance for whichever use the BR are applied.
Thus a seating area today is a seating area tomorrow even though on Tuesday it may be used for standing. But on Tuesday, it has to comply within a different part of the regs.
I stand to be corrected but there are no regulations for a 'combined seating and standing' area for stadiums. It simply hasn't been envisaged in the UK. There may be in the future but more likely the perfectly good regulations which exist for each will apply to each. The very good reason for this is the regs are built up from empirical research - from what has worked and what has not worked on the past.
This appears to differ Peter.
http://www.eaststaffsbc.gov.uk/Services/buildingconsultancy/Pages/BuildingRegsWhatisamaterialchangeofuse.aspxBuilding Regs: What is a material change of use
A material change of use is where there is a change in the purposes for which or in the circumstances in which a building is used, so that after the change the building or part of the building-
is used as a dwelling, where previously it was not;
contains a flat, where previously it did not, or a building containing flats is altered so that there are more or less flats than existed previously;
is used as a hotel or boarding house, where previously it was not;
is used as an institution, where previously it was not;
is used as a public building where previously it was not;
is not an 'exempt building' where previously it was.
When a material change of use takes place, the building, or affected part, needs to be upgraded to satisfy certain important parts of the Building Regulations. Fire safety, ventilation provision and energy conservation applies to all the cases above. Structure, weather resistance, fire spread and sound insulation apply in specific cases.