All of which explains why Thatcher was considering leaving the EU. She no doubt considered that the trade element might have worked, but with every increasing integration on the horizon, then from her point of view, the 'politics' wouldn't. Also there is no doubting this aspect spilled over into the Brexit vote as well. Historically the UK may, (or may not) have a 'special relationship' with the US, but it has never even imagined that kind of relationship with the EU as such. The UK didn't join the Euro-zone, it negotiated various opt outs and demanded rebates, and was generally seen as being the 'awkward squad' by many in the EU.
Ironically had Thatcher followed her impulse and gone for a referendum on leaving the EU, with her recommending that based on either Maastricht and/or Lisbon Treaties we should leave, then she would probably have lost it; because the general level of interest in leaving in the UK at that time was not much above 20-30%, much the same as when the original vote was taken in the mid seventies. Two of the foremost Europhiles in the cabinet, Heseltine and Clarke won their battle (as they saw it to stay in the EU) by managing to oust Thatcher, hence preventing a referendum that finally came some twenty years or so later. Unfortunately the remainers thought they were facing the same situation... and well, the rest is history!