It is all Class G airspace. That IAIP entry must be the result of someone with delusions of grandeur. Probably the same jobsworth who dreamt up the Mickey Mouse 'Land's End Transit Corridor which is a declaration of an AIAA to all intents and purposes. I'm surprised at the CAA printing it. Far better to be in direct RT contact with an appropriate agency should the worst happen.
Talkdownman - don't be such an idiot.
Filing a FPL is highly recommended for a sea crossing such as this, no one is saying you have to do it.
Even if it is short it is over as tricky sea conditions as you'll find, even on a nice day.
The FPL merely means that the details of the intended route, how many on board and what emergency equipment is on the aircraft can be made available at very short notice to those who, hopefully, will never have to fish you out of the water.
Anyone who has ever had to make a forced landing in the sea will tell you how unlikely it is that you'll have time to transmit this information, just as anyone who does do SAR will tell you how invaluable FPL information can be in making the difference between recovering someone alive and finding a corpse.