Just to back up what folk here are saying, I think that the RN SEA DART SAM destroys itself under certain circumstances.
TTL, there have been rumours around that during the Falklands war, Maggie asked Mitterand for the "secret codes" that could disable Exocet, she threatened to Nuke` Buenos Ares if she didn`t get them....Yes, I know!!!
I can certainly see the UK MoD asking Aerospatiale how best to defeat it though, even though the RN had Exocet anyway and would almost certainly have known how best to disrupt it. Chaff worked wonders, as long as you saw the missile coming.