Was it Stoneleigh Colour Laboratories, I think they are/were in Laemington Spa near Warwick, I used Colab in Coventry by post and 3H in Birmingham (a satellite lab of Colab) when in the city. Colab was owned and run by the Hartley Brothers maybe taht's where the H in 3H came from.
The Photocolor kits were superb I used the C41, RA-4 and E6 kits, they went out of production because Tetenal were awarded the contract to manufacture Kodak colour chemistry and that obliged them to cease manufacture for Ilford and Paterson (who by then owned Photocolor).
The issue was you needed to use the kit's on a regular basis to be economical or you wasted chemistry. I was regularly processing XP1/2 in Photocolour II most weekends as labs wouldn'tor were very reluctant to push process the films and it made sense to do my own E6, again often with the specialist Kodak and Fuji push process films.
Ian