I normally traveled in business suit but no tie. One trip through the then-new current Stansted terminal I experimented with tee-shirt and jeans. That was a different experience! Although the security people were not actually rude it was a bumpier trip than I was used too. When I was paid to roam around the USA fixing computer software problems I had several sharp instruments in my kit -- including a scalpel and a pack of blades. Never was asked about those!
Today, well later this month actually, I'm on Eurostar. Not quite the '80s experience, there's a 30 minute queue for check-in to get on the thing, but I'm happy to pay the premium over going through Stansted.