This is true, but the fact a 'partner' in the EU had sold a devastating weapon to your enemy, whilst you were in an armed conflict situation and which specifically resulted in the subsequent loss of HMS Sheffield and the lives of many UK servicemen/women, was what had first put doubt in Thatcher's mind and into her questioning our role in the EU. The enmity that arose between her and Delors that you refer to came much later and was what probably became the point at which she was openly arguing with members of her cabinet about withdrawing from the EU. Its also what contributed to the plotters ( supposedly and initially involving John Major) but behind the scenes Heseltine and Clarke were being credited as the ring leaders. When Heseltine and Major, perhaps realized they might be 'in with a shout' for PM if Thatcher was to go, they both pulled back a bit, knowing in Tory Party tradition 'he who wields the knife, rarely gets to wear the Crown' . Geoffrey Howe was the one who 'did the deed' with his famous speech from the backbenchers.
