I am now BA Gold. But was BA silver last November when I flew AA econ to St Maartens via JFK. I was prebooked MCE on the LHR-JFK-LHR sectors I was offered upgrade to J during online check-in both ways: £325 outbound and £275 return. I took up the offers and they were well worth it. Only catch I earned econ tier points 35 each way rather than 140.