It is actually a rule in Westminster that you can’t get a rare burger. Apparently chopped meat is a very different proposition than steak concerning foid safety. I like rate burgers but I don’t fault Longhorn for insisting after having argued this out with Byron.
I did not like Longhorn burgers, though, because like many burgers in the UK, they had all sorts of extra seasonings. Hamburgers should be just meat. Only Byron has hamburgers that satisfy me as US person. Sadly none in South London that I know of.