WHEN The Mill (20 July) started its first series, this time last year, it was derided by the critics; the public, however, rather liked it. Now it’s back, with the formula essentially unchanged: some characters have moved on, but it continues to be grim up North. The series is said to be based on documentary evidence about Quarry Bank Mill in Cheshire in the 1830s. But there is also plenty of fiction; the writer, John Fay, is a veteran of Coronation Street. The television Quarry Bank is owned by the Greg family  and now run by a younger son, William (Andrew-Lee Potts), a handsome martinet who has been given a fictional history of interfering with the mill girls. Meanwhile, mill engineer Daniel Bate (Matthew McNulty) is campaigning for the workers; at the same time, cheap labour