Sorry mate i removed your link to that particular site....here,s 2 grouts that you can use....both can be bought at that site you linked.....
BAL Superflex Wall Grout
A brilliant white, water & frost resistant cementitious wall tile grout with built-in admixture to give increased flexibility and high bond strength. Suitable for grouting porcelain, marble, natural stone, glass and ceramic mosaics, glazed and fully vitrified tiles. BS EN 13888 CG2 Grout.
BAL Microflex Wall Grout
A White cementitious tile grout especially formulated with built-in Microban® antibacterial protection to inhibit the growth of bacteria, such as Listeria, Salmonella, E-coli and black mould. It provides an added level of hygiene protection in bathrooms, showers and food consumption areas. The grout also has built-in admixture to provide flexibility and to enhance the bond to the edges of tiles and mosaics. Conforms to BS EN 13888, Type C, Class G2.