All members of the House of Commons are subject to be called upon to serve on Select Committees, being chosen for the purpose by a Committee of Selection, and the work thus done outside the actual Chamber adds considerably to the daily labours of politicians. No member may refuse to serve, if called upon to do so, and when, in 1846, Mr. Smith O'Brien declined to sit on an English Railway Committee, he was confined in the Clock Tower in the custody of the Sergeant-at-Arms.

The whole House can also resolve itself at any time into a Committee, when its function becomes one of "deliberation rather than inquiry."[378] Every Public Bill not referred to a Grand Committee must be considered in a Committee of the Whole House, and, indeed, the greater part of each session is occupied by this stage of legislation. The Committee of Supply and the Committee of Ways and Means are both "Committees of the Whole House," and are appointed to discuss the financial projects of the Government, the one to supervise expenditure, the other to devise taxation.

A Committee of the Whole House differs in no respect from the House itself, save that it is presided over by a chairman in place of the Speaker, and that the mace is removed from the Table. There are also some changes in the procedure of debate, as, for example, the cancelling of the rule forbidding a member to speak twice on the same question.

The idea of forming the House itself into a committee has developed, like so many parliamentary institutions, gradually and almost unconsciously. In days when the Speaker was too often the spy of the King it was considered advisable to get rid of him, and this could best be done by turning the House into a Committee and putting some other member in the Chair.

The Chairman of Committees in the Lords, and the Chairman of Ways and Means, or his deputy, in the Commons, takes the Chair when the House is in Committee, but it is permissible for either House to nominate any one of their number as a temporary Chairman.[379]

As a substitute for Committees of the Whole House in the Commons, two large Standing Committees, sometimes called Grand Committees, numbering from sixty to eighty members, are appointed to consider respectively all Bills relating to Law and Trade committed to them by the House. Besides the smaller committees already referred to there are Sessional Committees, appointed for each session, consisting of from eight to twelve members—as, for instance, the committee on Public Accounts, which meets once a week to look into the department of the Auditor-General—which control the internal arrangements of the House; and joint Committees of the two Houses, which discuss matters in which both are interested.

In the Lords also Standing Committees were instituted in 1889, but these were to supplement and not supersede the Whole House Committee stage, and after an experience of more than twenty years have proved their insufficient utility, they were abolished on June 24, 1910.

In the sixteenth century committees generally met outside the House, in the Star Chamber, in Lincoln's Inn, or elsewhere, but they have not done so for many years, numerous committee-rooms being nowadays provided within the precincts of the House.

At the commencement of every session the House of Lords elects a Chairman of Committees from among its own members. His duty it is to preside over Committees of the Whole House, or over Select Committees on whom the power of appointing their own Chairman is not expressly conferred. He is a salaried official of Parliament, and receives a sum of £2500 a year for his services. Similar duties are undertaken in the House of Commons by a Chairman of Committees and a Deputy Chairman, at salaries of £2500 and £1000 respectively.

The Crown usually appoints by commission one or more Lords to supply the place of Lord Chancellor, should that official be unavoidably absent. On emergency it may be moved that any lord present may be appointed temporarily to sit Speaker. In the House of Commons the Chairman of Ways and Means and the Deputy Chairman are similarly empowered to replace the Speaker when absent.