IIRC when I joined CAA as a trainee ATCO in '73 the lateral separation on the pond was 120nms.
Also Eric Woods in his book mentioned above gave '63 as the date that navigators, as opposed to pilot/navs, were dispensed with.
I have no axe to grind as it happened while I was still at school and 2 years before I joined the RAF, but it seemed with hindsight a strange decision. Several of my pilot mates joined BOAC having worked hard to get their CPL/IRs etc and were immediately sent on a 6 month nav' course. The result was surely that, now having 3 pilots on the 707s and VC10s, the time to command must have doubled.
When those types went out of service in the late 70s lots of pilots were laid-off for 3 years while the backlog was worked through and presumably recruiting at the bottom must have stopped.
There was always a ready supply of trained professional navs leaving the RAF, I for one would have loved to join BOAC as a nav when I left the RAF in '73, even though the career may have only lasted until 1980( the date I believe BCAL went from navs to INS ). I bet the bean-counters at BOAC didn't have a say back then.