Laws are first parliamentary bills in either the House of Commons or the House of Lords. A bill is a project of law. When bills are approved and voted in Parliament, they become laws. There are four main types of bills. First, there are government bills, that are the most important forms of legislation. Government ministers introduce them and such bills represent government policy. When governments have a significant majority, government bills almost invariably become laws. Second are Private Members’ Bills, that are introduced by individual Members of Parliament or backbench MPs, or peers of any political party. They are not likely to become laws because less parliamentary time is dedicated to discussing such bills. Third are Private Bills, that are proposed by an individual or organization (associations, companies, local communities...) seeking specific, usually local, powers. This is a kind of bill that is presented to Parliament in the form of petitions. Last, there are Hybrid Bills that are Public Bills and that may be introduced by the Government or by a backbencher. Such bills are rare.
Bills are first debated in the House of Commons by MPs. Then they go to the House of Lords for further discussion by Peers. Suggestions for revisions and amendments are offered for all legislation but financial bills (related to taxation). Both chambers must agree on all amendments. The House of Lord can delay legislation but not reject laws outright. If Peers do not approve of a bill, the government can present it to the monarch for Royal Assent, which is actually a mere formality. After Royal Assent has been granted, a mandatory step, a bill becomes an Act of Parliament and goes on the statute books. It is to be noted that there is no judicial review of laws in the UK.
