There is a grain of truth in the story, as there often is. It was not the Gannet airframes they were after but the AN/APS 20 AEW search radar. As has been mentioned there was a total lack of AEW equipment in the RN and, just as skips had been rifled for refuelling probes and bombing computers for the Vulcans, someone hit on the idea of retrieving these radars and fitting them to Sea Kings to provide AEW cover.
It never happened of course but the scheme did live on, using the very modern Thorn EMI Searchwater instead we got todays Sea King ASaC.7's from this germ of an idea.