Manchester United forked out £37.1million on Chelsea's Juan Mata this weekend in a deal that surprised the football fraternity.
England's biggest clubs rarely do business with each other as they are scared of strengthening a rival side.
However Chelsea were prepared to sell Mata to whoever offered the most money and that turned out to be the Premier League champions.
Following Mata's move to Old Trafford, we have decided to look at the most expensive transfers between English sides.
Click through the following pages to see who makes the list.
Who turned out to be a valuable signing and who failed to make the grade at their new club after moving for big money? Feel free to comment in the box below.