I came across "more's the pity" in Catherine Alliott's Not That Kind of Girl. There's a passage where she goes over an exchange between a salesperson and herself. The salesman asks which pack of Silk Cut cigarettes she'd prefer. 'Impotence?' 'Please. Marvelous.' He grinned. 'Doesn't come with a guarantee, you know?' 'More's the pity!' I learned the phrase means "unfortunately," and also found it in titles such as "More's the pity about the Tuttles' Farm." How does this phrase work though? How did it came to mean what it means?