At the 2005 general election Penning stood in the Labour-held seat of Hemel Hempstead, narrowly defeating sitting MP Tony McWalter. Penning overturned McWalter's 2001 majority of 3,742 votes and won the seat (after a partial recount) by 499 votes. In July 2007, Penning was promoted by Conservative Leader David Cameron to the post of Shadow Minister for Public Health.
