Though it's worth remembering that London Information almost always want an ETA..... they'll want an ETA at the FIR boundary. Judging by the number of times I hear them say "Let me know when you have it" on a sumy weekend day, not a lot of pilots know that.
Yup, I didnt know that and was asked by London info over the weekend, couldnt snap back with an answer either as it didnt figure as needed in my plan, plus the 'ETE Next' on the trusty GPS was cherbourg, not the FIR boundry....
Regards, SD..