The Westminster parliament comprises two ‘houses’: the House of Commons (the lower house), consisting of 650 members (MPs) elected by their constituencies, and the House of Lords (the upper house), consisting of life peers, hereditary peers and Lords Spiritual (bishops of the Church of England).
At present the House of Lords has 775 members. The purpose of parliament is to govern the country in the monarch’s name and this falls to the largest party in the Commons (or a coalition of parties as at present). Legislation, once passed by the Commons goes on to the Lords.
The upper house can scrutinise and delay legislation but since the Parliament Act of 1911, the Lords cannot reject it. The government is primarily responsible to the House of Commons and the prime minister stays in office only so long as he or she retains its support.