From my experience most Brits are horrified when they learn about all the stuff we immigrants have to go through just to live here. Of course, they assume that those of us from the dominions/former colonies have a free pass. They have no idea what the actual rules and regulations involve.
That's been my experience. Everyone assumes that my wife can just get on a plane and come live in the UK (I'm UK citizen born and raised in the UK). They're absolutely shocked when I tell them we needed 65 grand in cash savings, and nearly 1500 pounds for the application ... and then need to do the same again in 2.5 years.(I don't have a job offer in writing for the UK so cash savings was our only option).
To be fair most Americans assumed that when I married my wife I would immediately become a US citizen. They know little of I130 adjustment of status, advance permission to travel, waiting 2 years for a green card, HIV testing, TB testing etc. Nor do they know that admitting to having smoked marijuana in your youth could get you permanently disbarred from the US, spouse or no spouse (one of the most ridiculous aspects of the war on drugs)
As a Brit living in the US for 18 years I've found Americans extremely friendly and welcoming. I sincerely hope my wife will find the same of my fellow Brits when she arrives in the UK at the end of this month.