Most of the appliances in England run on a 220 volt system. Their plugs are usually big clunky items. A user can have a nice flat laptop like an AirBook - but the almost fist size created a large lump in their computer bags.
The new plug folds flat - when opened and twisted - it converts into a three prong 220 volt plug that is very safe and does not require an adapter.
Note that most outlets on the walls in England have a switch turning the outlet off before you plug and unplug and item. Higher voltage plugs tend to arc more than American ones. 220 volt systems require much thinner wire.