You will need to get permission from Special Branch
Actually you just need to inform them. There is a form called....can't remember, GenDec or something.....which you fill in and fax off to your local SB, and thats it. Stuff like names and addresses, passport details etc. A word of advice, fax this off EARLY, ie a day before, if you end up not going, no worries, but if you leave it too late I'm sure you'll be getting the latex glove treatment on your return. If they want to visit you, the'll pop over before you leave, if no-one shows up, you know you are good to go.I do one of these for France as well, it is not needed but it you make a habbit of it you don't forget, and SB probably just chuck it in the bin.
Then just the FPLN as normal. Get a FIS or something across the channel, and then contact Jersey zone at least 10nm north of 50°N who will clear you in SVFR. They'll want to know an estimate of 50° N.
Rgds
EA
PS Anyone know where i can download a General Declaration??