Complex sentence: Originally, the M65 was planned to go via the town centre of Blackburn, but opposition by the local council effectively killed this plan off, which was cancelled by the Thatcher government in 1980 until the 1990s.
Split into simpler sentences: Originally, the M65 was planned to go via the town centre of Blackburn, but local council opposition effectively killed this plan off. It was cancelled by the Thatcher government in 1980, and not re-entered into the roads programme until the 1990s.