Private Members' Bills are Public Bills that are introduced by back-benchers. Any MP can introduce a Bill on any day by informing the Speaker that he or she wishes to do so but there are a number of formal ways in which this can be arranged, some of which increase the chances of the Bill becoming law, while others increase the profile of the issue being raised.
Each Session a certain number of Fridays are set aside for private members' Bills. These are the days on which private members' business is said to have precedence – government business has precedence on all other days. On the second sitting Thursday of a Session a ballot of back-benchers is held. The top 20 drawn will have precedence in time allocated to private members' Bills. In this way, the MPs drawn first has the best chance of seeing their Bills progress. Normally, the 20 Bills brought forward by these MPs are introduced on the same day (the fifth sitting Wednesday of the Session).
Although MPs do not need the permission of the House to bring in a Bill, they can use the Ten-Minute Rule, in which they formally seek the consent of MPs to introduce a Bill. In practice, because the procedure takes place at the beginning of Public Business, the MP requesting permission to present a Bill secures 10 minutes in Parliamentary 'primetime' to make a speech on the subject of the Bill, raising the profile of the issue. Another MP may speak in opposition to the proposal and a division may be held. If permission (leave) is given, the Bill is introduced immediately, but it joins the ranks of private members' Bills not selected in the ballot, which have little chance of becoming law.
Even Bills that have benefited from the ballot have no guarantee of progressing. MPs, including Ministers, can use a number of tactics to halt their passage and, as ever, the most common and most powerful is time. MPs will frequently seek to 'talk out' private members' Bills to which they are opposed. Proceedings on Bills that have not concluded at the Moment of Interruption are adjourned and go to the back of the queue for private members' business, effectively wrecking their chances of becoming law.
The Government can always adopt a private member's Bill if it wishes. This means that the Bill is allocated Government time and is much more likely to become law.