Why have Tony Blair and David Cameron been chatting?

Tony Blair and David Cameron were once rivals

"There are three classes which need sanctuary more than others: birds, wild flowers and prime ministers."

So said Stanley Baldwin, a Conservative Prime Minister three times in the 1920s and 1930s.

Does Mr Baldwin's observation help explain the relationships that can exist between serving and former prime ministers?

The Daily Mail reports that David Cameron has struck up a "special relationship" with Tony Blair. Both Downing Street and Mr Blair's office dismiss the report as overblown.

But one source close to Mr Cameron suggested to me that any sitting prime minister would regard conversations with his or her predecessors as "special," simply because there are often no more than a handful of previous prime ministers alive at any one time.

Mr Blair has visited the prime minister's country retreat, Chequers in Buckinghamshire, to see Mr Cameron - invited back to the very place that for 10 years he could think of as his own.

'Four jobs'

Many of the discussions between the two men, we are told, were arranged because of Mr Blair's role as a Middle East peace envoy representing the US, Russia, the European Union and United Nations.

But the conversations would stray onto other aspects of politics - and doing a job so few other living people have done.

Previous occupiers of 10 Downing Street have reflected on the unique nature of the job.

"The British prime minister has four distinct jobs: running the government, leading his party in parliament, leading the national party and being a constituency Member of Parliament," wrote Sir John Major in his memoirs.

"By contrast, the President of the United States does not run large chunks of domestic policy, rarely attends sittings of Congress, does not lead the national party and can delegate to the Vice-President," Sir John added.

"Bill Clinton's staff once proudly told mine that they were limiting him to a maximum of 60 hours' work a week. Mine would have been happy to limit me to one hundred," he reflected.

Little wonder Sir John didn't like comparing notes on workload with his peers at summit meetings abroad.

Get it?

There are currently just five people alive who know what it is like to be prime minister: Lady Thatcher, Sir John Major, Tony Blair, Gordon Brown and David Cameron.

It is perhaps the ultimate gig where the job is the lifestyle and the lifestyle is the job.

Combining that with the facts that a very limited bunch know what it is like to do it, and one day it will suddenly end, means it is perhaps inevitable there is the potential for a connection between prime ministers past and present.

Take these two telling quotes from the former Conservative Prime Minister Harold Macmillan.

"Nothing rolls up more quickly than a red carpet."

"Ours is a pretty unrewarding life."

The second observation, reports historian Peter Hennessy in his weighty tome The Prime Minister: The Office and its Holders since 1945, is what Mr Macmillan said to Selwyn Lloyd on appointing him Chancellor in 1960.

Harold Macmillan paints a picture of the potential for a lonely existence. Or, to put it in language more suited to 2012, when people ask what it is like to be prime minister, it is inevitable not many people "get it".

'Weight of office'

Gordon Brown invited Lady Thatcher to Downing Street for a cup of tea.

But it doesn't appear Mr Brown and Mr Cameron have each other on speed dial.

And Lady Thatcher and Sir John Major, despite being in the same party, had their famous public spats after her departure from Downing Street.

Maybe too many years of direct political combat, or public criticism once a successor is in office, limit the potential for convivial chat.

But, as the former Labour cabinet minister Lord Adonis reflected in a letter to Peter Hennessy whilst working in Downing Street in the late 1990s, ultimately there is more that can unite prime ministers present and past than divide them.

He pondered whether his then boss, Tony Blair, worked harder than William Gladstone, four times a Liberal Prime Minister in the mid to late 19th century.

"He does different things. Lots of time on planes, in meetings and doing media interviews - but little time in the House of Commons and virtually no debating. But that doesn't affect my point - that the weight of the premiership is no heavier than in the past, and that the difference between prime ministers lies in personal temperament and ambition, not weight of office per se."