muckles:
Margret Thatcher wasn’t anti EEC/EU she wanted the trade benefits, but was more skeptic about its social polices. During the 1980’s leaving the EEC was Labour Party policy, not the Conservatives.
Leaving the EEC was also ‘Labour’ policy during the 1970’s assuming you followed people like Shore,Heffer and Benn not Jenkins,Wilson and Callaghan.
As for the Cons they were always for the EU unsurprisingly if you replace Unionist with the word Federalist which means the same thing. 
On that note exactly what so called trade benefits.Other than those which,like Heath and Callaghan,she handed over on a plate to the EU with a rocketing trade deficit to prove it.While no self respecting Nation and leadership worth the name would allow itself to be blackmailed along the lines of sovereignty for trade regardless.As I said there are some massive questions which need answering here up to head of state level.