Tony Blair will today go to Buckingham Palace to tell Queen Elizabeth II that he is stepping down as her Prime Minister. Then will go Gordon Brown and she will make him the next Prime Minister.

Constitutionally, the monarch can invite whoever she pleases to be Prime Minister. However, constitutionally it would be madness not to take advice and so the Queen asks the departing Prime Minister who she should call to invite to form an administration - though we know that that's almost certainly going to be Gordon Brown.

Royal Tradition: How Brown Gets The Job

By Alastair Bruce
Royal Commentator
Tuesday June 26, 2007

So, we all know that Gordon Brown is going to be the next Prime Minister - but just how does he actually take hold of that office?

The Queen holds the power

The answer is through a process that gives us an insight into the history of the appointment, the nature of power in the constitution and reminds us exactly whose 'Prime Minister' he will be.

He will only actually become Prime Minister when he is invited to do so by the Queen.

In fact, she will first ask him if he can command a majority in the House of Commons - to which the answer this time is an easy "yes" - and then she will invite him to form her Government - to which the answer will also be "yes".

With this second affirmative reply, he will become Prime Minister and invested with the Queen's executive powers to rule in her name, subject to Parliament, with leave to form her Government by recommending all her Cabinet and other Ministers.

To start with, as Gordon Brown has been painfully aware of for more than a decade, Tony Blair needs to relinquish the appointment first. To do this, the serving Prime Minster must seek an audience of the Queen.

Audiences between Queen and Prime Minister usually take place every week but can be arranged whenever required at a mutually convenient time.

As this particular handover is so well forecast, the Queen's private secretary will have approved the timings requested by No 10 Downing Street, in order to ensure Her Majesty is available.

After a general election, this process can be somewhat rushed, as one party looses power to another, and the defeated Prime Minister must go and offer his, or her, resignation to the monarch.

Constitutionally, the monarch can invite whoever she pleases to be Prime Minister. However, constitutionally it would be madness not to take advice and so the Queen asks the departing Prime Minister who she should call to invite to form an administration.

And so, Tony Blair will go to the palace and be introduced to the Queen by the equerry, Commander Heber Acland, as "The Prime Minister, Your Majesty".

Behind closed doors the Queen and Tony Blair will cover the formalities of recommendation and resignation before discussing family, 10 years of service and retirement (his, not hers), before the Queen presses a bell and the equerry returns to take plain "Mr Blair" to his car.

Tony Blair: On his way out

It will probably be his own car because the Prime Ministerial car - with all the advisors, police and trappings - has been stripped away by the audience. And there is temporarily no Prime Minister.

Before long, Gordon Brown, with his wife, will be driving to the palace. They will be received at the door by the same equerry and led upstairs to the Queen. This time, he will be introduced as "The Right Honourable Gordon Brown, Your Majesty".

At the moment of the Queen's invitation being accepted, Mr Brown's dreams of power will be fully realised and when the door opens, the equerry will be the first to say, "Congratulations, Prime Minister".

Traditionally the description of this event is very formally reported in the court circular. It will inform us that the Right Honourable Gordon Brown had an audience of the Queen and "kissed hands" upon his taking office as Prime Minister and First Lord of the Treasury.

It may go on to say that he was presented with his seals of office. In fact, there is no ceremony of kissing hands - this tradition of fealty was dispensed with long ago, though it still takes place in a representative form when privy councillors are appointed by the Queen.

Gordon Brown: New man for the job

The seals of office are the symbols of power given to each Cabinet minister. They were once used to validate documents with royal authority.

In the following days, after the new Cabinet is appointed, there will be a stream of cars bringing Tony Blair's old ministers to the Queen to deliver up their seals of office for the Queen to redistribute to new Cabinet ministers that Mr Brown has recommended.

Remember, it is the Queen who appoints Cabinet ministers on the advice of her Prime Minister.

The Queen will give Mr Brown the ancient powers of another, much older appointment, which all Prime Ministers hold. This is as First Lord of the Treasury.

This was first granted by William the Conqueror to Odo, Earl of Kent in 1066 and it had great power then as it does now. This is because whoever held the money could influence the power.

Sir Robert Walpole was already First Lord of the Treasury in 1721 when he developed the role of the monarch's Prime Minister, as the "first among equals" in the evolving ministerial system of Cabinet Government.

Although the term 'Prime Minister' was regularly used from the end of the 18th Century, it was not formally established until 1937. Therefore the letter box on the door of No 10 Downing Street is still engraved "First Lord of the Treasury".

Becoming Prime Minister is a path of constitutional steps, culminating in the invitation of the Queen to be her prime minister. Once selected to be the Queen's prime minister, Mr Brown, as head of Government, is ours as well - for as long as he commands a majority in the Commons.