The rules were correctly enforced. The limit of 100ml applies unless the liquids are medically necessary during your flight or a reasonable amount of delays. What the TSA may or may not allow is irrelevant to the UK and it is incumbent on travellers to establish the requirements in each country they fly to or through rather than assuming their own country's rules apply. Nobody you complain to will care more than to send a form letter reply.

That said, the rules are stupid.