The 13A clause is only for floors other than the ground floor in single occupancy, so on at least one floor they could get away with selling 2 (of course you could just put a single high performance foam extinguisher in at negligible extra cost)
Too many firms quote BS5306-8 as law which of course it's nothing like - the DCLG guides even shy away from it for smaller premises so you can't BS them by saying the enforcers insist on full compliance.
A professional non sales oriented assessor will use the BS as a starting point but apply their skill in providing a premises specific assessment of need.
I'd point out to the client they needn't provide any of the stuff at all by law, but if they really want to have extinguishers etc despite that then they could have x, y & z
Also I wouldn't be sticking dirty great extinguishers in - 13A rated 2 litre high performance foams or water additives (no need for B cover) or better still a 2 litre Wet Chemical or ABF rated foam so that it can be used on a chip pan. (As the users are not going to be trained I don't want them blasting a CO2 into a fat pan because in real life they wlll choose the smallest lightest extinguisher and not read or understand the pictograms)
I have great pleasure in helping clients in ripping up so called 'surveys' by extinguisher suppliers and cut by two thirds the requirements in one particular building (a common trick is to take a plain concrete fire escape only stair and put PFE on each landing despite the risk area on the occupied area of the storey exit just 30cm away having tenants fire points)
