In the 60's and 70's BEA aircraft procurement department had a great reputation for specifying requirements on new aircraft which subsequently made them very poor sellers compared with their American cousins. The Trident was a good case in point - it would have been a worthy competitor to the 727 if Hawker Siddley had been left to their own devices.
The BAC 1-11 was similarly "modified", happily only in the 18 examples specifically ordered by BEA. The theory was that since the aircraft was to be used mostly with the then new Jetways the forward integral airstair was deemed to be surplus to requirements and removed, leaving only a small step which was mechanically operated by a lever adjacent to the door once opened. The neccessary mods were ordered and doubtlessly handsomely paid for by BA but the c of g was found to be unacceptable. The answer was to mould around 300lbs of lead to fit in the airstair well which was carried about until the scrap man called (gloating?) and cost significantly more than leaving the airstair as it was intended to be.
The irony was that for the first 7 years of service most of the fleet was based either in Manchester or Tempelhof neither of which had jetways in those days, neccessitating the purchase of many more sets of steps than would otherwise have been the case! In the 14 years I flew these aircraft we had forward steps provided on a vast majority of occasions and where a jetway was available they had to be modified with a special cut out in the leading edge of the platform to fit around the door thus allowing it to marry up to the aircraft floor or a movable "plank" which fitted onto attachment points in the aircraft step so the pax didn't fall down the 6 inch gap to said step.