It still sounds very complicated. Doesn't the UK need talented people? Or are they getting enough from mainland Europe?

It's a painstaking and time consuming process. There's a huge talent pool within the UK and mainland Europe however given the tech/start-up commonalities between the UK & US, it would make an enormous difference if the process of hiring from the US was simplified.

Just as long as it a quid pro quo the other way for green cards UK - USA.

When I test it, it looks all good. Have you visited the website before? Possibly your browser has cached an old version of their certificate.