How many Labour leaders have won elections since the Second World War?

The answer is just three. As Labour agonise over their UK defeat and humiliation in Scotland, it is worth reflecting on which leaders demonstrated how to win elections, and whether anything can be learned from their success.

The three Labour poll-busters were Clement Attlee, Harold Wilson and Tony Blair.

Mr Attlee won just a single election, but arguably the most important, in 1945, when he led a peacetime Britain through rationing and economic stress to oversee the creation of the National Health Service and the welfare state.

Mr Wilson won four elections (1964, 1966 and twice in 1974) and surprisingly lost another, in 1970. And then there was Mr Blair. Love him or hate him, he won three in a row in 1997, 2001 and 2005, the last two years after the invasion of Iraq.

It is generally held that Jim Callaghan might have halted Margaret Thatcher's momentum and avoided the "winter of discontent" by going to the polls in 1978 rather than the following year, when an embattled Labour administration literally ran out of time.

Thirty years later it seemed that Gordon Brown had learned nothing from the Callaghan experience. He swithered when those around him were urging a dash to the polls soon after forcing out Mr Blair in 2007.

Why does this matter? Well, Labour might learn from its three election-winning prime ministers.

Mr Attlee, that quiet, purposeful politician of a bygone age, pressed his case for a new Britain while running against Winston Churchill. Mr Atlee tapped into the large and growing sentiment of a Britain exhausted by war and eager for change, for victory to mean something, to be exploited in a way that rewarded everyone for the sacrifices of the war.

His party represented real hope to men returning from war and their communities at home: equality of opportunity, health and welfare safety nets, better housing, a clean break from the past and a future that meant the war had been worth the fight.

Two decades later, Mr Wilson stood for bright new future in the face of a tired, sleaze-ridden and doddery Tory party led by an aristocrat who'd left the Lords.

Mr Wilson consorted with the Beatles. He understood economics. He spoke of real social change at the height of the Swinging Sixties, the "white heat" of new technologies. He won twice, before surprisingly losing to the brittle Edward Heath, and won twice again in 1974 as his rival faltered in the wake of bitter strikes and the imposition of the three-day week.

Then there was Mr Blair. In 1997 "things could only get better" after 18 years of Tory rule. New Labour was slick, its merciless pursuit of Tory voters breath-taking, its popularity massive.

Contrast that with Mr Callaghan's "crisis, what crisis?" Or, much later, with Mr Brown's insistence that the financial crisis of 2008 was nothing to do with his "light touch" regulation and the rampant behaviour of banks.

Then there was Ed Miliband. Does anyone know what Labour has stood for since 2010? In their post-election humiliation, what do Labour feel they should do if they are ever to recover?

The consensus seems to be that they should be more right wing in England and more left wing in Scotland. This is as loopy as a 1980s Labour conference motion and just as likely to succeed.

Talk of separate Scottish and UK parties is very dangerous for Labour, and anyone awaiting a federal solution to the UK may well be better setting aside time to sniff a little coffee.

Nobody ever doubts what the Conservative Party stands for. The only variation is how far its adherents think they should go in promoting neo-liberal economics or opposing a centralised Europe.

Look at the SNP since last year's referendum. What do they stand for? "A stronger voice for Scotland", said Nicola Sturgeon on TV, in public, or gazing down from all those roadside posters.

Five words, with a few variations; as effective as the campaigning Attlee, Wilson or Blair and much more memorable than whatever it was Mr Miliband and Jim Murphy appeared to dream up on almost a daily basis during a car crash of a campaign.

Confused former MP Tom Harris despaired on election night: "People wouldn't listen to us." Yes, voters can be very frustrating indeed. Or perhaps they didn't know what it was that they were supposed to be hearing, and gave up trying.

Labour's soul-searching might start from that point. There are few votes to be won by girning in public. People need a credible, positive and deliverable vision. History tells us that is what wins elections.