as an Oceanic Controller, I can confirm that what my Scottish Hi-level colleague says is correct. The clearance you get from us is based on the initial estimate given - if that is changed due wind etc. by 3 minutes or more then you SHOULD call again on our VHF CDO freq's or on HF to check whether your new time is OK or not. However, in the above stated circumstance, the Shannon controller would have passed that revision onto us for you and, if your clearance changes they will tell you.
THis only works if you tell the Adjacent ATC centres to pass the revision to us i.e. Scottish / Shannon / Brest / Madrid.
You would never have got us on VHF to do it yourself because you would probably be outside our CDO's range near Shannon.
Points of Information - a CDO is a Clearance Delivery Officer based at Prestwick - an assistant who receives requests and issues clearances as decided by the controllers.
The people you talk to on HF are RADIO OPERATORS based at Ballygirreen just north of Shannon.(i.e. not controllers) They act as relays for all our messages to you and yours to us.
Shanwick controllers only ever talk to other controllers - pain uh?