Simplify the following text for a Grade 11 native English-speaking person.
Original: It operated high-speed express train services on the East Coast Main Line from 1996 until the takeover in 2007 of the franchise by National Express East Coast on 9 December 2007 .
Simplified: It operated high-speed express train services on the East Coast Main Line from 1996 until 9 December 2007 when the franchise was taken over by National Express East Coast .