However as he is both the Responsible Person and the only Relevant Person then he is the master of his own destiny and I dont think any enforcement measures could be made to stick under the RRO.
I see no reason why enforcement measures wouldn't stick.
To answer SidM:
The owner is indeed a relevant person at night if he can be affected by a fire in the shop.
If it were being built now then escape through the shop would not be allowed by Building Control.
If it were being built now then 60 mins separation would be required at the building stage. No linked alarm would be required if this were the case.
Since it is built and up and running, as Kurnal points out, the risk assessment should determine what is necessary. But taking an enforcers viewpoint, I would certainly not be happy with escape through the shop, and in lieu of 60 mins compartmentation linked part6 smoke alarms are usually accepted as a reasonable solution.