Complex sentence: Christchurch, and in particular Mudeford, had been enjoying a modest tourist trade since King George III had patronised the town in the 1790s but the arrival of the railways made Christchurch accessible to many more potential visitors.
Split into simpler sentences: Christchurch, and in particular Mudeford, had been enjoying a modest tourist trade since King George III had patronised the town in the 1790s. The arrival of the railways however made Christchurch accessible to many more potential visitors.