Complex sentence: The GCR line was the last complete mainline railway to be built in Britain until section one of High Speed 1 opened in 2003 and was also one of the shortest-lived intercity railway lines.
Split into simpler sentences: The GCR line was the last complete mainline railway to be built in Britain until section one of High Speed 1 opened in 2003. It was also one of the shortest-lived intercity railway lines.