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.