Project Cancelled by Derek Wood has a whole chapter on this. It's an excellent read, and a fantastic insight into post-war British defence procurement, and how countless opportunities were lost - the Hawker P.1081/1083 for one...
The HS.681 was to use RR Medway engines, not Bristol Pegasus engines, at least initially. These engines would have some means of altering the direction of the jet exhaust, to improve the short-field capabilities (STOL, not quite VTOL) of the type, but for patent (or copyright) reasons this was called 'thrust deflection' and not 'thrust vectoring'.
When the project was on the verge of cancellation, an 11th-hour attempt to save the project involved the airframe from the HS.681 and the wings and engines from the HS.801 Nimrod, the project being named the HS.802. The Wilson government went with the C-130K instead.
There was also a project to mate the fuselage of the Shorts Belfast with the wings and engines of the C-141, the project being the SC. 4/50.