Complex sentence: A Great North Eastern Railway InterCity 225 train bound for Leeds had left London King's Cross at 12:10, and was travelling at over when it derailed south of Hatfield station at 12:23.
Split into simpler sentences: A Great North Eastern Railway InterCity 225 train bound for Leeds had left London King's Cross at 12:10. It was travelling at over when it derailed south of Hatfield station at 12:23.