Ah ha, The television programme I am trying to dredge up may be "Quick before they catch us". The description of the first story line suggests to me that they may have built a camera obscura which, apart from the theme tune, is the only thing that I remember about it. The actors do look familiar, but then they look like every British actor in the'60s! Hmmm, it is listed at TV Cream (go to PQ and scroll down), where the theme tune is clearly not "catch us if you can", but I can see why I might be confused about this, since they are nearly contemporary songs. I think this might definitely be the one. Of course it has been wiped so we'll never know will we? I think that the line that it was based on a book by Mark Timlin has to be wrong since the Mark Timlin book of the same name appears to be published in 2000 and he looks way too young to have been writing in 1966. But I suppsoe it may be a reprint and an old photograph.