Thanks gents
Would 6mm backerboard be OK? I could go with the 12mm backerboard but from reading some lit it seems that the 6mm comes in 1500 x 900 which would mean only 4 panels needed for my 2500 x 1800 floor as opposed to 5 of the 12mm 1200 x 900. That supposes that it is these sizes held by Topps. I would probably have to cut them down to 1250 at Topps in Swindon to get them in the Polo though.
I might also be going for Granfix 1 Part CFTA adhesive instead of the BAL as non-trade prices look a lot better. I can get 20kgs for £16 but I doubt non-trade BAL SPF from TOPPS will be anywhere near this low, will check tomorrow. Have to go and have a wisdom tooth out now so as much as I try; tiling is not the order of the day
Cheers
Neil