"it is to be set in a northern mill-town"

 This novel is Hard Times, published in Household Words from April 1854. It is set in the fictional town of Coketown, based on Dickens' visit to Preston. The novel explores themes such as utilitarianism, factory working conditions, and trade unionism, but has had a mixed response from critics since its publication. The novel was John Ruskin's favourite of Dickens' work, but George Bernard Shaw later criticised the accuracy of its portrayal of trade unions, and more generally questioned Dickens' understanding of the underlying social issues.