I would propose a Britannia as the attached extract (currently the complete drawing is for sale on Ebay) shows a very similar looking tip of the tailplane plus the relatively close location of the curved rear passenger windows (on some versions only). This would allow the photo to be taken with a reasonably wide angle lens that would include the end of the tailplane.
I note that according to Wikipedia, Britannia's were flying passengers with Monarch up to 1974. However it appears that they must have usually flown from Luton as their bases at Manchester and Gatwick did not open until the 1980's
