zonoma - When EGTT hands us to EISN the login passes over to the Irish. So whatever method we log in with London carries forward and we are unable to swap.
Its interesting to think about the 40 sec restriction on FANS though. During the climb out from London we get our Oceanic clearance via ACARS which pops up on the same screen as the CPDLC clearances - We normally have a quick think about that clearance and print it prior to clearing it, so the FANS clearance could be sitting 'behind' that leading to the 40 second restriction timing out... Nothings perfect is it!