By Rob Neil
BBC Money Programme
The announcement has finally been made: the Blairs are leaving Downing Street. But at only 54, will Tony Blair be reaching for his pipe and slippers just yet?
Once he leaves Number 10, Tony Blair is entitled to an immediate prime minister's pension of £63,000 and he will still earn a MP's salary of £60,000.
Added to this, Cherie Blair, as a leading QC, is estimated to earn a six-figure salary. But even with this joint income, they could struggle to meet the payments on mortgages of £4.5m.
However, the Money Programme has calculated the Blairs could make £10.5m in the next 12 months.
In 2004, the Blairs took out a 95% mortgage on a £3.65m townhouse in Connaught Square near Hyde Park, London. This year, they bought the adjoining mews house for £800,000.
These two purchases - combined with the £200,000 remortgage of their Sedgefield constituency home, Myrobella, in 2003 - mean they now have interest payments of more than £20,000 a month.
This is almost as much as the average annual salary.
But if the successes of past prime ministers are anything to go by, Mr Blair need not worry.
Sir John Major has reportedly made £1m a year since he left Downing Street, while Lady Thatcher amassed a fortune after she stepped down in 1990.
Many experts believe that Mr Blair's earnings could dwarf those of Sir John and Lady Thatcher.
If he is looking for ideas on how to make serious money, then there is an example across the Atlantic.
His good friend Bill Clinton left the White House in 2001 with an estimated debt of $12m (£6m). Since then, he has turned his retirement into a money-spinner worth between $10m and $50m.
Mr Blair's strongest asset is his image as a world statesman.
As Giles Lury, brand consultant at The Value Engineers, points out: "He shouldn't rest on his laurels by just telling the story of the Blair Years."
Mr Lury also suggests that "having a worthy cause is, in marketing terms, a great thing for him to be doing".
The Blair Foundation
And it seems that the groundwork for this is already being laid.
A US businesswoman and confidante of Mrs Blair, Martha Greene, has registered the Blair Foundation website, which will be used to promote his good causes.
Ms Greene is also organising the refurbishment of the Blairs' Connaught Square house.
Although dwarfed by the philanthropic spending of billionaires such as Bill Gates and Warren Buffett, the Blair Foundation, like the William J Clinton Foundation, could raise a vast amount of money.
But although the foundation may emerge as Tony Blair's main passion, it will not directly help to pay the bills.
Tony Blair could make more money as a speaker than Bill Clinton
Both Sir John and Lady Thatcher took up positions in the City, but surprisingly, the £75,000-a-year salary for five to six days' work a month may not make financial sense for Mr Blair.
Top City headhunter Betty Thayer says Blair is "never going to get rich being a non-executive director".
With the income that it would bring, "it just wouldn't be possible to live the kind of lifestyle that he is used to."
In addition, the fact that Mr Blair is the longest-serving Labour prime minister means he may not want to be too closely associated with big business.
So it is unlikely he will head to the City just yet.
However, it is likely he will follow Mr Clinton's lead and sign up with one of the big American speaking agencies.
In 2005, Mr Clinton earned just less than $5m for 29 speeches - and it has been reported that he has earned almost double that in 2006.
Last year, on one particularly lucrative day in Canada, Bill Clinton made $475,000 for two speeches. This was more than double his annual salary as President.
Wesley Neff, president of the New York-based Leigh Speaking Bureau, thinks Mr Blair's future as a speaker is "bigger than Bill Clinton's", since "he will be the first world leader to come on the market in the last three or four years".
Mrs Blair has already appeared on the professional lecture circuit. She reportedly charged £100,000 for a tour of Australia and £30,000 for a single event in the US.
Later this year, she is scheduled to appear in Toronto, Vancouver, San Jose and Denver, on a bill with Mary Robinson, Erin Brockovich and Hollywood celebrities Goldie Hawn and Sigourney Weaver.
Although ticket prices of $60-$80 are not as high as some, Martin Dunn, editor of the New York tabloid Daily News, thinks that in the States, "Hollywood, politics and money are so interrelated that it will do Cherie's standing the world of good being alongside famous faces".
Mr Neff thinks that in one year on the lecture circuit, "between the two of them, the Blairs could probably make in excess of $5m."
So if the money begins to roll in, Tony Blair might have time to indulge his creative side.
Although experts think he would be prudent to avoid the bearpit of shows like Have I Got News For You, he could follow Al Gore's success and make a documentary feature about some pressing world issue.
But as John Smithson producer of the hugely successful Touching the Void points out, even though An Inconvenient Truth grossed $42m at the box office, it is unlikely that Mr Gore saw much of that, because of the "madcap economics of the film business".
However, "at the end of the day", as former editor of The Sun, Kelvin Mackenzie, states, "his banker is his book."
Top literary agent Eddie Bell, who handled the Thatcher, Major and Gorbachev memoirs, thinks Mr Blair's advance for his autobiography could be "in the region of £8m".
He says it would be a guaranteed best-seller: "It will sell whether it's on Richard and Judy or not."
The Money Programme: The Blair Rich Project, Friday 11 May at 1900 on BBC Two.