Simplify the following text for a Grade 12 native English-speaking person.
Original: Stop Stansted Expansion ( SSE ) is an advocacy group established in 2002 as a working group of the North West Essex and East Herts Preservation Association , in response to the Government 's consultation on expanding UK airports and , particularly , expansion plans for Stansted Airport subsequently defined in the Air Transport White Paper in December 2003 .
Simplified: Stop Stansted Expansion ( SSE ) is a pressure group established in 2002 . It was originally a working group of the North West Essex and East Herts Preservation Association , in response to the Government 's consultation on expanding UK airports and , particularly , expansion plans for Stansted Airport defined in 2001 .