fire door width is 710mm. two escape routes. discount the largest which is 720mm. Maximum fire protection measures in place roof over 3m but under 4m, no more that 77 persons occupancy as confirmed by the client. is this acceptable or not based on the variations 20% principal. it is not a new build. 

Technically not as the traditional benchmark has a 750mm absolute minimum and BS9999 has an 800mm absolute minimum even though it builds in flexibility. However in existing legacy builds a bit of common sense is required (especially as it's not that far below and the PAS79 FRA methodology allows a bit of leeway) and so the risk assessor should look at the premises, precautions, risk profile and see if they are comfortable justifying the situation in their FRA and that the Responsible Person is happy to accept this.

Also see BR 2019 Escape over flat roofs Para 2.31 - 2.32

Any one observing people in the U.K. today would acknowledge the terrible blight of obesity. As far as I am aware, the number of folk that could move through a unit of exit width of 550mm was determined post 2nd world war by the number of gendarmes that could pass through per minute. Turned out to be 40 thus it was contended that if a building was to be evacuated in 2.5 minutes, a unit of exit width would allow for 100 persons. By extrapolation, a standard 1050mm door width would permit 200. 
That original model has been adjusted somewhat but as far as I can see, it is still employed. I bet not one single gendarme was a fatty with mobility issues!