Before WW2 Ilford Limited was mainly a manufacturer of sensitised materials. They had a brief encounter with Dufaycolor but once the war started government directives prevented any further research into colour techniques. By contrast Kodak in the USA had forged ahead and produced their Kodachrome colour transparency film and by 1942 had also produced Kodacolor negative film and was marketing and offering a processing service for these materials. These materials were at the time, during WW2, only available in the USA.
After the war in 1945 Ilford Limited lost no time and a small team started to research colour processes. Despite having access to FIAT - CIOS and BIOS reports, http://www.cdvandt.org/fiat-cios-bios.htm the possibility of using a similar process to Agfacolor was dismissed because of the difficulties in producing the colour couplers that this system needed. But by 1948 the team had produced a non-substantive colour transparency film called Ilford Colour D. The "D" stands for daylight; other light sources would need filters to get the correct colour balance. They got around patent issues that clashed with Kodachrome by the inclusion of a silver sulphide barrier layer and a colloidal silver barier layer. Ilford Colour D had a speed of 8 ASA like Kodachrome.