Martin is correct, you'll need to jerry can it from the local petrol station.
TBH it's going to be possible but hard work... it's not going to be the odd 25 ltrs is it? After a run across the channel and a day's fishing I'd gues you'll need at least 100 ltrs. That has to be carried, taxi, and then transported back across the harbour and decanted on the water.
Needs some thought - as said, Mark will offer advice - he runs petrol in his Raider.
Alternative is Guernsey, as they have Petrol in the marina, but as stated it's further on still.
People also need to start thinking of accomidation as Mark can only take 5.