When there is an international transfer, the buying and selling clubs have to register it on the FIFA Transfer Matching System (TMS) in order for international clearance to be generated.
The buying club have to upload all the information to the system and the foreign club have to match all the details.
The English FA will request clearance and as long everything matches; the foreign association will issue clearance to The FA, who then informs the club and League.
The Premier League receives a copy because it needs to ensure that players coming in have had their registration transferred to this country, or Wales in the case of Swansea City.