I'm pretty sure that this bike was one that they made in the basement, I think the ones they had made outside were less idiosyncratic (as I remember them as a child in the early '80s, and as google seems to back up) - that Ballantine photo and that article make me think that it could well have been built by Harry Healey there.

Perhaps the lamp bracket puts it a bit earlier than Ballentine's bikes, so maybe late '60s. Seems plausible. There have I think long been UK laws requiring the use of lights on bicycles, but I think it's only in the last few years that policemen have started upholding those laws.

As an aside I had Richard's Bicycle Book as a boy, and it got me tinkering with bikes. I just ordered an old copy.