Colin owner of Freightdog seriously looked at making a conversion but it was deem too complex.
From Secret Projects Forum:
The project of an AEW version of the H.S. 125 was much earlier than 1988. It is mentioned and illustrated in the January 1983 issue of AIR INTERNATIONAL entitled "From Skyraider to Nimrod... Thirty Years of British AEW" by Mike Hirst, which clearly identifies it as a 1964 project.
In 1962 this British team looked at three AEW configurations — respectively with ventral, dorsal and forward-and-aft-scanner system (FASS) installations. In trade-off studies, the latter arrangement was assessed to show the best overall performance, although it was hardly the most elegant-looking solution. With these results in mind, the Blackburn design team of 1963 (by then a part of the Hawker Siddeley Group) proposed the P.139 project. With hindsight, this unlovely-looking aircrfaft can be viewed as a sensible proposition, but its bulbous proportions earned it disparaging nicknames, and its stability proved to be suspect in wind-tunnel tests. By 1964, the P.139 project had been shelved, and less-expensive designs, using existing airframes, were being considered.
One serious idea was the conversion of several examples of the HS.125 business jet, but its configuration meant that it had to use a fixed dorsal radome, like the out-dated Tracer, and it was unable to meet even the simplest endurance requirements. It too was shelved, having brought home one other very important technical truth, that the FASS radar had to be used, as proposed in the P.139. [...]
In February 1965 Britain cancelled all future aircraft carrier development, and this effectively killed all interest in shipborne AEW developments.
