Certainly no "clever british plot".
There were certain "things which could not be" in german military research regarding U-Boats:
- Enigma is unbreakable
- Centimetric radar is impossible
To understand why it is important to know that military science was one of the weak points in Germany. While Germany did produce some amazing new weapons, a military research did not happen in the organized fashion as in the US or Britain.
German technological breakthroughs were either result of company work (jet engine) or charming individuals (Walther Submarine, Rocket Program) who were able to sell their work to high ranking officials.
Each branch had their own engineering departmen, which was staffed with people from the military or the military administration, but not real scientists.
Also it was strongly personalized:
Radar, like Codebreaking, had just one person in charge who simply sought to cover its back. It was like that with Admiral Maertens who always assured Doenitz that Enigma is unbreakable, it was like that with General Martini who was in charge of Radar development.
Of course that one brit told them this story, it was believed because it was an explanation that did not involve the "impossible" centimetric radar.
The best german scientists (or better, the best german scientists without von Brauns or Walthers marketing talent) spent the war at the universities, not working for the war effort. Konrad Zuse designed his first programmable computer in his living room and nobody official EVER gave a damn about him. In Britain he would have been "invited" to Bletchley Park in no time.
In any chase, it did not really do any harm as Metox was useless against centimetric radar, so it did not provide any warning at all.
So wether you left off Metox because of fear of detection or because of knowing it was useless did not really matter.
Of course it might still detect older metric ASV sets, but these were replaced pretty fast. Long ranging Uboats in the indian Ocean or the Brazilian coast might have put metox to some use, as the aircraft there did not get top of the line radar as soon as those in Britain or Iceland.
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