I worked for them at 247 Burlington Road New Malden.
Decca Navigator in the mid 1970s made radar equipment for yachts and small vessels at Ingate Place Battersea.
The research labs in Burlington Road were by that time designing VOR (VHF OmniRange) air navigation beacons. These were still in use as late as 10 years ago - I was in a light aircraft from Deauville to Shoreham which was using that system around 2008. Like the 1940s Low Frequency system this would no doubt be superseded by GPS now.
Another facet of Decca Navigator was the Electronic Warfare establishment in Hersham. I don't know exactly what they did - I was not given the tour. I had told them I was in CND at university.
The old Decca Navigator system seemed to have a sort of camaraderie. There were transmitting stations all over the world with only one or two employees - rather like light houses. There used to be a Yahoo group run by these people, but it seems to have been shut down. I think Yahoo stopped these groups (which were message boards a bit like Urban).
However clearly a few keenies have kept it up here:
Deccaman groups.io Group