Yes that's correct
see the section
02 UuA on BA only flight, booked through a travel agency
The country in which the TA is in must be the same as the address in your BAEC profile for you to be able to UUA. So if your TA is in the USA and booked the tickets from there, and your BAEC profile is in UK, unfortunately you're out of luck.
UUA - BA is not an airline that allows UUA at the airport though cash ones may be available.