flash8
I will answer as it relates to BOAC and leave the BEA answers to somebody else.
The Hamble course was 18 months. BOAC/BEA also trained pilots at Perth and Oxford although the course was shorter (1 year?).
The failure rate at Hamble was about 30%, although much smaller at Perth and Oxford. 48 started on my Hamble course and 32 finished.
Pilots joining BOAC went on to either the 707 or VC10.
After simulator training, up to two weeks of aircraft base training were completed which included about 40 landings.
Pilots had to complete a full Flight Navigators course and obtain the red licence. One of the co-pilots would have to navigate on Nav sectors whether they were SO, FO or SFO.
Two years were spent as SO (one stripe) followed by a further eight years as FO (two stripes). SFO (three stripes) came after ten years in the company. Time to command varied between nine years and twenty years (unfortunately twenty in my case).
It was not easy to transfer to BEA until the merger when it slowly became possible.
In 1969 BOAC produced an excellent film showing the training of a BOAC pilot, from starting the course at Hamble to completing his line training. There are some excellent shots of the VC10 during his base training at Shannon.
Hope this helps
Dave