What is the position in terms of works that don't comply with an approved design under the JCT DB 2016 form of contract?

An Employer lets a contract to built a multi-storey car park and during the design submissions by the Contractor the exit width of the staircases are set out on drawings in compliance with relevant legistlation and planning/building control requirements. The Employer approves the design to status A.
During the build steelwork columns are situated in slightly different positions at the site for technical reasons and the result is that the exit points at the stairs at ground level are slightly narrower than on the Contractors approved design. The Employer rejects the staircase area citing both aesthetics and health and safely concerns and requests defect rectification work but the building control officer during final sign off approves the staircases as constructed as the stair entrances are clearly within legal limitations and are still adequate for access.
Is the work around the staircase defective on the basis it deviates from the Contractors approved design but neverthless appears to meet the requirement of the Employers Requirements which merely required a functional car park approved by the planning and building control authorities?