It's a very small island so you need to build a trireme pretty quickly. Personally I don't have land starts where I lose my first chariot before I have 6 cities typically, whereas unless I'm putting a city on every tile in England I have to discover and build a trireme, then send settlers to the mainland. If I'm trying to expand to the mainland I have to deal with the fact that Europe gets covered fairly quickly with some of the French, the Germans, the Russians, and the Romans around and competing for that space. Also a nuisance is that the AI often kills some of the neighboring civs before you can meet them and trade techs.
The disadvantage is slightly bigger than having to build one trireme though, because if you want to keep building settlers on the island you need to be able to transport all of them.
England is a worse start on many subsequent real world maps though, especially Civ V where not being able to move settlers until optics is a pain, especially since that means you have to delay getting bronze/iron/animal husbandry/writing to get optics. Furthermore, England is smaller on those maps, and min-city distance is a factor.