On May 6 2009, the House of Lords debated and approved a Bill that made it a crime to display tobacco products on open view in British shops (thus creating 'the dark market').

One aspect of the debate was the cost to shop-keepers of re-fitting their premises to comply with the law. In December 2008, the government estimated that it would cost the average shop £1,000 to do so. With a vote pending in the House of Lords, it was in the interest of the anti-smoking lobby to convince peers that the cost would be considerably less than that.

This is the story of how they went about it, made possible by the Freedom of Information Act, under which dozens of previously unseen Department of Health e-mails have been made public.