Thatcher was part of the problem, frankly.
Years after leaving office, she declared the EU unreformable, corrupt, socialist etc. but she never advocated withdrawl. Everything she later said about the EU was obvious in the mid 1980’s but she never did anything about it.
While in office she appeased pro europe scumbags in the Conservative Party while detroying her political capital on second tier issues like the Community charge.
That may be but I feel awful for the British people.
Few people remember that it was Thatcher who virtually invented the single European market for goods and services. Before her intervention, the Common Market was restricted to goods, not services, and not even all categories of goods. Thatcher persuaded an initially reluctant EEC (as it then was) to accept the universal single market, using the civil servant Arthur Cockroft as her negotiator.
It was just one element in her grand scheme to turn the UK from a manufacturing-based to a services-based economy.