The UK has many political parties, the main three being Conservative, Labour and Liberal Democrat. These three work in both the House of Commons and House of Lords.
Political parties in the Commons
In addition to the main three parties, the Commons has a range of other political groups also elected by the public. This includes nationalist organisations like Plaid Cymru (Wales) and the Scottish National Party, Northern Ireland's various political parties and minority parties like the Green Party or Respect.
Political parties in the Lords
Outside of the main parties there are a small number of Members that are not affiliated with a main political party and those belonging to minority groups. In addition there are a limited number of Church of England archbishops and bishops and the Crossbench Peers group.
The Crossbench Peers group is currently the second largest group in the Lords (after Labour); and is formed by independent Members who don't take a party whip - which means that they are not told how to vote by a political party.