They should have just done the obvious… chosen one of the other options for making an AEW Nimrod:

http://www.spyflight.co.uk/nim%20aew.htm

Eventually, UK scientists deciding to ditch the FMICW radar in favour of the pulse-Doppler radar and funding for the system was finally approved in 1972. Various options for the Nimrod airframe were considered; the first option involved mounting the E-2C AN/APS-125 radar and associated avionics above and inside the airframe. The second option was to use the AN/APS-125 radar with British avionics. The third option was to mount the AN/APA-171 radome and antenna on the Nimrod, with Britain supplying the radar transmitter, receiver and avionics. The fourth option was an all British radar and avionics system, with some American components, and a FASS with pulse-Dopper processing operating in the S-band. Although this option provided the greatest input from British industry, it also carried the greatest technical risk and the alarm bells should already have been ringing. But, as in so many UK defence fiasco’s over the years, political decisions, namely keeping BAe & GEC workers employed and retaining AEW radar technical expertise in the UK, overcame the many doubters and outweighed common sense.

By the end of 1974, instead of purchasing an off-the-shelf system with a proven track record, the Labour government predictably decided on the fourth option, the Nimrod AEW 3, accepting whatever extra cost and technical risk that involved. At the time the Labour government also considered that joining a possible NATO purchase of the Boeing E-3A was just too politically complicated, expensive and subject to unknown delay – which is rather ironic considering how things eventually turned out. At this point it was widely reported that the RAF was in favour of a dedicated UK purchase of the E-3A, rather than the Nimrod, but the cost, together with the potential loss of jobs in some marginal Labour seats, was always going to mitigate against this option.

http://www.secretprojects.co.uk/forum/index.php?topic=1272.0
Aircraft with APS-125:

Nimrod AEW.3 variants:

Nimrod-E-2C fit: