Ardex is excellent grout, my favourite is gk for solid floors but they are fazing it out and replacing it with ardex FL with a vast array of colours. Or another one l have been using is tilemaster which is a dream to work with.
Ardex is excellent grout gk is my favourite but they are fazing it out and replacing it with ardex FL with a vast array of colours, tilemaster is good, kerrakoll, or the old school option of quartz sand and cement.
Evening Phil, I'm in Mossley Hill so will happily pop by to give you a bit of advice if needed though the guys on here know what they're talking about! Deffo listen to Lithofin Bob, Lithofin products are generally spot on. I've used the cleaners and sealers for years. The only other impregnating sealer I would recommend is Dry Treat tho this is considerably dearer. As for grout, as previously mentioned, Tilemaster is superb. Biggest issue I can see there is getting the old gear out. Original geometric floors were often butted together so removing grout without damaging the tiles is a pig! To be honest and imo if you get the cleaning process right the grout is most often restored to a good level.
What l did after the first stage that is outlined, is got a dremell or similar with a fine blade for masonry, went through quite a few blades mind you and took ages to rake it out minimum 2mm. Regrouted and resealed using stainstop. lt is worth the effort good luck