If brain recalls correctly, US 220V sockets are 3 pin, so I'm thinking this is a 110V plug and lead intended to be plugged into 110V socket and is attached to an appliance that tolerates 240V (or has an internal switch setting). None of which means it is an approved mains flex for UK or that the appliance is double insulated, but it could be both.220V is not on standard outlets in the USA