I have vague memories of the children's television series Raven and even of owning the paperback novelisation of it, but in truth I was a bit old for that sort of thing by 1977.
A bit of googling finds this video and a summary of what it was about:
Raven, a 15-year-old Borstal boy, is released on probation to live with Professor Young, an archaeologist immersed in research into Arthurian legend, and his wife, an amateur ornithologist. The professor is working in deep underground caves whose carved symbols suggest that King Arthur may have used them as a hiding place, and Raven is intrigued by his belief that Arthur was not one man, but a succession of chiefs...And it turns out to star Phil Daniels and Michael Aldridge, who also played Percy Alleline and Seymour Utterthwaite.
Nice pyjamas, Phil.