Re: A strategic decision....
"If you read the news... in the US... it appears that the UK Ambassador to the US was leaking classified information."
Either the US news media read it wrong or you did. The ambassador's reports were confidential. What was leaked - by someone else - was his actual words. I doubt many would consider what he was reporting was a secret - we can work that out for ourselves from POTUS' own pronouncements.
I'm sure all the other ambassadors have made similar reports - I'd love to know what the French said, for instance.