If a bill is considered of great constitutional importance, or if very fast passage through Parliament is required, then it may be scrutinised in the Commons by a committee of the whole House.
This means that any MP can contribute to the clause-by-clause consideration of a parliamentary bill takes place after it has passed its second reading.
Usually, bills are examined at committee stage by a public bill committee, outside the Chamber, where only MPs on the committee can contribute.
But when a bill is debated in a committee of the whole House, the mace is placed on a bracket underneath the Table of the House and the chairman of ways and means stands in for the Speaker.
The Finance Bill is always sent to a committee of the whole House in the Commons.
In the House of Lords, committee stage consideration nearly always takes place in a committee of the whole House.