Came across this only today. It’s from 2005.
P Bowles from Littlehampton, West Sussex wrote
On September 27, I arrived at Heathrow to check in for a flight to Boston with Virgin Atlantic. As we stood in line, our passports were checked by an agent. I have a full British passport, but my place of birth is Baltimore. I was taken to see a supervisor, who asked whether I had proof I had given up my US citizenship. Apparently, a British passport is not sufficient proof. Virgin said it could not fly me unless I produced a “Loss of Nationality” letter.