Britain's newest MP Sarah Green was sworn in today following her surprise victory in the Chesham & Amersham by-election.
The Liberal Democrat was welcomed to Parliament by party leader Sir Ed Davey and his deputy Daisy Cooper.
Ms Green overturned a Conservative majority of more than 16,000 to win by 8,028 votes. The by-election followed the death of veteran Tory MP Dame Cheryl Gillan.
The Liberal Democrats campaign focussed heavily on local opposition to HS2 and the government's proposed planning reforms.
Labour hopes to capitalise on unease among Tory backbenchers in a debate in the Commons calling for changes to the proposed planning rules to allow communities to object.