Earlier this week, I explained the formalities that a person must undergo before they can become Prime Minister. Today, I will do the same thing for the other members of Her Majesty’s Government. This is a surprisingly complex subject since ministers take office in many different ways.
Most Cabinet ministers formally take office at a meeting of the Privy Council. There are three oaths/affirmations involved: the Privy Counsellor’s Oath, the Oath of Allegiance, and the Oath of Office (however, if someone has already taken the Privy Council Oath and the Oath of Allegiance, they will not need to take them again). The oaths are taken while kneeling on little footstools, and afterward ministers kiss Her Majesty’s hand. Sometimes the gymnastics involved have proven too much for ministers. Richard Crossman records an incident where four Privy Counsellors found themselves on the wrong side of the room and ended up crawling toward the Queen on their hands and knees.
The Lord Chancellor, the Lord Privy Seal, the Chancellor of the Exchequer, the Chancellor of the Duchy of Lancaster, and Secretaries of State receive seals of office after taking the oaths. Well into the twentieth century, outgoing ministers were expected to surrender their seals to the Sovereign in person upon leaving office, but this practice has been replaced with a more flexible procedure whereby ex-ministers receive a ‘farewell audience’ at a convenient date. If a Secretary of State is being appointed to a new position, they will be given placeholder seals (when Crossman became the first Secretary of State for Social Services in 1968, he received the seals of the newly abolished Secretariat of State for Commonwealth Affairs covered in sticky tape!). Unlike the other ministers, the Chancellor of the Duchy of Lancaster always takes the Oath of Office and receives the seals after the Privy Council. The reasons for this are obscure—Professor Brazier has suggested that it’s because of the ‘personal character’ of the appointment (the Duchy of Lancaster is the Monarch’s private estate).
The Lord President of the Council is simply declared as such by the Queen and then takes the oaths and kisses hands.
Oddly enough, British ministers generally don’t receive any kind of official document when they take office. However, there are some exceptions. The First Lord of the Treasury, Chancellor of the Exchequer, and Lord Privy Seal are all appointed by Letters Patent (the Chancellor’s appointment is actually effected by two separate instruments—one appointing them as Chancellor and Under-Treasurer and one appointing them to the Treasury Board along with the Prime Minister and the Junior Lords of the Treasury). The Chancellor of the Duchy of Lancaster receives Letters Patent under the Seals of the Duchy and County Palatine, and the President of the Board of Trade is appointed by an Order in Council (nowadays, this position is always held by the Secretary of State in charge of trade).
With junior ministers, the appointment process is simpler. They take office as soon as the Queen approves their appointments, though they’ll have to take the Oaths of Allegiance and the Oath of Office in the presence of another minister (usually the Lord President of the Council). The Law Officers and the Paymaster General are the only junior ministers who receive instruments of appointment. Although the Law Officers take office as soon as Her Majesty approves their appointments, she will confirm them in office by Letters Patent. The Paymaster General will receive a warrant under the Royal Sign Manual. Most junior ministers don’t get to meet with the Queen on their appointment. However, Government whips in both Houses of Parliament are traditionally given sinecure offices in the Royal Household. Commons whips become the Vice-Chamberlain of the Household, the Treasurer of the Household, and the Comptroller of the Household, while Lords whips become Lords/Baronesses-in-Waiting. The Vice-Chamberlain, Treasurer, and Comptroller receive a white staff as a badge of office, but their colleagues in the Lords don’t receive anything.
UPDATE (6/30/22): I’ve discovered that the Chancellor of the Duchy of Lancaster receives Letters Patent rather than a Warrant under the Queen’s Sign Manual so I’ve altered the text accordingly.
 Richard Crossman, Diaries of a Cabinet Minister: Lord President of the Council and Leader of the House of Commons, 1966-1968 (London: Hamish Hamilton and Jonathan Cape, 1976), 44.
 Richard Crossman, Diaries of a Cabinet Minister: Secretary of State for Social Services, 1968-70 (London: Hamish Hamilton and Jonathan Cape, 1977), 233.
 Rodney Brazier, Ministers of the Crown (Oxford: Clarendon Press, 1997), 84.
 Their duties in the Royal Household are purely ceremonial. Commons whips serve as the channel of communication between Her Majesty and the Commons, while Lords whips greet foreign VIPs on behalf of the Queen.
 These staves will be ceremoniously broken over the Queen’s grave at her funeral.