You're right that Morleys supports the B£ and is a decent local/independent business. But let's be absolutely clear - Topshop in Brixton is run by Topshop, the staff are employed by Topshop and the profits made there go to Philip Green (or, more accurately, his wife) without proper tax being paid. The fact that Topshop rent their shop space off Morleys is neither here nor there.
How do you know? If it's a typical concession arrangement the staff would be employed by Morleys, a Morleys manager would run the operation and Green would just get commission on what they sell. The scenario you describe is highly unlikely - it's equivalent to Morleys subletting part of their store to Topshop.