Building control Dilemma?

I planned an internal remodel of a flat that I own that included removing load bearing walls, chimney breasts etc and generally making the flat more open plan. The flat is U shaped around a central communal stairwell, such that you enter through a hall, then into the kitchen, then into the sitting room, then into the bedrooms.

Originally there was a wall between the kitchen and the sitting room, but my scheme involved removing that wall to make an open plan sitter/kitchen. I submitted plans to building control and they approved them, contingent on installing linked fire alarms and an adequate fire break for the bedrooms given that the only exit was through the kitchen. In stripping out the flat and preparing for the installation of RSJ’s an old doorway was uncovered that linked one of the bedrooms with the communal hall. The building inspector came and told me that I needed to retain the door linking the bedroom to the communal hall as a means of escape, despite previous approval that did not involve retaining this hidden door. I hated the idea of a doorway from a bedroom to the communal hall and so foolishly continued with my original plans, covered over the old doorway and finished the flat off without further inspections and without gaining a completion certificate.

Works were carried out in 2010, and now I want to find a way to regularize the works for all sorts of reasons, including tidying up my affairs for a sale. What options are open to me, how should I proceed? Is there a statute of limitations on building control? Are there other options open to me apart from reinstating the door, such as a localized sprinkler system in the kitchen area? This far down the line, can I persuade building control to accept their original approved plans, that is, without the door from the bedroom to the communal hall? Should I engage an independent building inspector to guide me with initial advice? Any advice and ideas as to how to proceed would be highly appreciated

Thank you

Edward