Queen Elizabeth Stadium, though the rental costs would be high.
But IMO a GP in London would sell well, fantastic transport links, plentiful hotels, if you can't afford Centralish hotels use public transport to travel out of the City.
London is a big draw for supporters from around the world. Who would probably make the GP part of a longer holiday to the UK and Europe.
Plan it ahead and invite Prince William, he likes motorcycles and lives locally, though I doubt we'd see him on the Jubilee line.