Since 1967 now I've had a think. Autair, Britannia and British Midland had been regular then for a few years, then along came Monarch in 1968 making it 4 UK airlines. Channel and Dan Air made it 6 in 1969. Channel didn't operate 1970-72 but we had Skyways in their various incarnations instead 1970-72. Invicta and Donaldson made it 8 UK operators in 1971.
Mind you, the total number of UK passenger airlines is barely half what it was in 1968. I can only come up with 11 now, compared to at least 20 in 1968. Numerous takeovers, mergers etc. coupled with the trend for non-UK registered airlines to set up major UK based operations have all had a big impact.
Last edited by cj241101; 7th Jan 2018 at 18:52.