Initially elected as a Conservative, she resigned from the party in February 2019, joining and later serving as leader of Change UK.
She resigned from Change UK in June of the same year, and joined the Liberal Democrats in October 2019.
She announced on 29 October that she would not stand for re-election at the next general election.Allen succeeded Andrew Lansley, the former Conservative Secretary of State for Health who had held the seat since its creation in 1997, following his retirement from the House of Commons in 2015.