I've now spoken to Farrow & Ball who tell me its skimming stone and wimbourne white.

If you scroll through this link you will see my photos. I ordered this for my kitchen. My completely inexperienced contractor installed the floors over existing 50 year old asbestos vinyl. We used the Atrafloor cold weld. The seam is almost invisible and the product is water tight. Your installers are using old technology and old methods. It is very usable for a home installation. Mine have been down about 3 months old and look great. My installer also made a small measuring mistake and I ended up with a 2nd seam, but it is not noticeable at all. You cannot use the type of adhesive sold in USA it is old fashioned and old technology. Mine was not stiff at all, but I did keep it inside the house to acclimatize before installation. It is soft a pliable. Atrafloor answered all my emails.

Be prepared to take out a second mortgage to pay for them!!! I spent a wonderful afternoon browsing around Chelsea Design Centre. The Ann Sacks store is glorious and more than a tad on the pricy side ;-)

Looks like Cornforth White by Farrow and Ball. Impossible to say from a photo but it may be worth a try.