It breaks my heart to be a cop about this, but some people have been committing the uncool sort of crimes.

Safety glasses that allow you to view an eclipse are coded ISO-12312-2. However, people have been putting that code on cheap sunglasses and then selling them as eclipse-safe. Unlike fake Versace stuff down the market, this fake has consequences: you can harm your eyes using them.

At the time of writing there are three manufacturers in the UK who can be vouched for: Sollunae, Absolute Eclipse and First Light Optics. Be careful when not buying their stuff.