Complex sentence: Flying Scotsman, due to Alan Pegler having secured a clause in the purchase contract when she was purchased from BR in 1963--the only opportunity to view mainline steam locos in operation after the ban was to be on privately owned heritage railways.
Split into simpler sentences: Flying Scotsman, due to Alan Pegler having secured a clause in the purchase contract when she was purchased from BR in 1963. After this, the only opportunity to view mainline steam locos in operation after the ban was to be on privately owned heritage railways.