Cheers for the additional information swaghauler
In regards to the British going for active guidance rather than IR, I have a vague recollection that at the time of development, early generation IR guidance was still a little "generous" in what it considered a viable heat source. That is to say, I think the British considered that IR wasn't sufficiently reliable particularly with the use of IR decoy flares as a countermeasure so they preferred to use another method.
Keep in mind I'm going from memory here so I'm sorry to say, I can't recall much more than that at the moment
