MPs and peers appointed by the Prime Minister to the Government are known as Ministers of the Crown. After the Prime Minister, the next most senior Ministerial rank is that of Secretary of State (this includes the Chancellor and any Deputy Prime Minister). The hierarchy is normally considered to be as follows, although a specific order of precedence is published after each reshuffle:
Deputy Prime Minister/First Secretary of State (not always appointed)
Chancellor of the Exchequer/Home and Foreign Secretaries (the 'Offices of State')
Secretary of State
Minister of State
Parliamentary Secretary/Under Secretary of State
Secretaries of State are empowered by Acts of Parliament. They are always members of the Cabinet and they tend to be privy counsellors as well. Secretaries of State head large Whitehall departments and have extensive policy and financial responsibilities. Apart from any ceremonial or historic significance, Secretaries of State who head 'spending departments' (those responsible for the majority of government expenditure) tend to be considered more important.
In a large Whitehall department, the next in line is a Minister of State, who might be thought of as a deputy to the Secretary of State, although larger departments may have several. Some Ministers of State head their own departments and some attend Cabinet Meetings. They tend to be given their own responsibilities within a department, with the agreement of the Prime Minister.
Other Ministers are either Parliamentary Secretaries (in a department where there is no Secretary of State or where the Secretary of State sits in the other House) or Under Secretaries of State. They have smaller, more specific responsibilities and there may be several in one department.
Both Ministers of State and Parliamentary Secretaries/Under Secretaries are commonly known as Junior Ministers. Because of the principle of collective responsibility, all Ministers, however junior, will be expected to back the Government in a Commons division or resign. This is known as the 'payroll vote' - it represents the minimum number of votes on which the Whips can rely.
Any change to a Minister's responsibilities or title requires the agreement of the Prime Minister. Ministers hold the position to which they have been appointed for as long as they have the confidence of the Prime Minister or until they resign.
Secretaries of State and Ministers of State are normally drawn from the Commons, where they can be accountable to MPs for their policies and spending.