It was what was called a BAC 1-11 which was one of only 2 aircraft types that had a built in passenger staircase at the rear literally between the 2 rear mounted engines
Add a few more to these types, others include the Boeing 727, DC-9 and Sud Aviation Caravelle.
Flew with Dan Air ( loved the use of Dan Dare) to Rimini in the early 1970's, asked to visit the flight deck which was the norm before the ban, was amazed by the pilot sitting there with his feet up smoking on his pipe.
great memories