No it's not BA policy to block taxiways ( but I can see why you might think that).
The BA policy is: Prior to doors being closed we are presented with a
provisional loadsheet (roughly speaking the latest best guess) to allow us to complete the loading of our Flight Management Computers with weight info. and also to allow us to check/confirm performance calculations. The
final loadsheet which reflects the actual load on board, should be then be datalinked to us shortly after pushback. We cannot takeoff until we have received these final "figures" - just in case the provisional/best guess figures were wildly wrong.
In theory
the final loadsheet should arrive very shortly after doors closed and not cause a delay.................however
in the real world delays are not unknown and then it gets very embarrasing, especially if you are blocking the only taxiway. Fear not, it happens at places other than CPT, and it even happens to other airlines - saw three jetBlues being pulled out of line for takeoff at JFK the other day because "numbers" delays.