Complex sentence: Darrowby is based on the real towns of Thirsk and Sowerby, but Askrigg, in Wensleydale, was used for filming scenes set in Darrowby in the series.
Split into simpler sentences: Darrowby is based on the real towns of Thirsk and Sowerby. It was Askrigg, in Wensleydale, however, that was used for filming scenes set in Darrowby in the series.