Photographs below of a Ceramic tiled floor in the kitchen of a house in the village of Houghton on the Hill near Leicester. The Ceramic tiles were fine but not unusually the grout had darkened substantially and would need to be deep cleaned to get it fresh again.
Cleaning Tile and Grout
The grout was badly stained so I decided to go with a strong dilution of Tile Doctor Remove and Go which we normally use for removing sealers but is also a very powerful cleaning product. It was run along the grout lines and tile and left to soak in before being scrubbed in with a black pad fitted to a rotary floor machine. The floor was then washed down with clean water and the process repeated until the grout was back to its original condition; the ceramic tiles looked much cleaner as well.
The tile and grout was left to dry and then then grout was sealed using Tile Doctor Ultra Seal which is a natural look sealer that I usually use on Travertine but works equally well on grout. You have to remember that the top layer of grout is actually porous and will attract dirt if left un-sealed, sealing it will ensure it keeps its appearance for much longer.
Source: Tile, Stone and Grout Maintenance and Restoration in Leicestershire