As I recall from our discussions when T5 opened, the original plan was always to mix everyone together in the retail halls. When T5 was being designed, the international standard was for in and outbound pax to be kept 100% separate. If memory serves, they got special permission to allow in and out pax to mix specifically for the purpose of retail.
History: The reason for BAA being so focused on shopping is that. When BAA was privatised, the Thatcher govt introduced a cap on how much they could charge in landing fees. The political intention was to show that costs could be brought down under commercial mgmt, rather than state ownership.
Since this heavily restricted their ability to make money - and make the investment that was so badly needed that the govt had not made - BAA changed other things.
Firstly, as I recall, they changed the way that carriers were charged. Originally, they had been charged by the size of the aircraft and a BAe 146 paid much less than a wide body long haul. This immediately upped the costs for all the domestic connecting flights and (it could be argued) helped to spur the lo-co market from regional fields!
Secondly, they turned to retail. They upped the cost to the shop keepers of the cost per square metre of floor space and that cost was passed on to the pax. Then they moved on to car parking ...
In due course, BAA became known as the largest retailer in the UK and made more money from retail than from handling aircraft. That is the context whereby T5 is what it is and (in another thread) someone is complaining about parking charges at STN.
It could be argued that this is all a rather amusing sequence of unintended consequences: A Conservative govt that always beats the drum of 'national security' created the circumstances whereby, 20 years later, security is compromised and people are endangered right the way down to congestion on escalators - because of saving money.
I sit to be corrected.