After the UK cabinet's recent foray to Aberdeen, Alex Salmond will enter the belly of the Westminster beast today. The Scottish First Minister will deliver the New Statesman lecture (sold out) on "Scotland's Future in Scotland's Hands" at 6:30pm. In the address, which is trailed in today's papers, he will urge the English centre-left to embrace Scottish independence as a "progressive" cause. As he said when the lecture was announced, he believes an independent Scotland would act as "a progressive beacon and a powerful economic counterweight to the pull of London", helping to "rebalance the social and economic structure across these islands which has seen the UK become one of the most unequal societies in the developed world". In a reversal of the assumption that Scottish independence would consign the rest of the UK to permanent Conservative government, Salmond's pitch is that a more "progressive" Scotland will help to create a more progressive Britain.

The First Minister is right to downplay the fear that the loss of Scotland would lead to unending Tory rule at Westminster. On no occasion since 1945 would independence have changed the identity of the winning party and on only two occasions would it have converted a Labour majority into a hung parliament (1964 and October 1974). Without Scotland, Labour would still have won in 1945 (with a majority of 146, down from 143), in 1966 (77, down from 98), in 1997 (139, down from 179), in 2001 (129, down from 167) and in 2005 (43, down from 66). What those who say that Labour cannot win without Scotland are really arguing is that the party will never win a sizeable majority again. History shows that England and Wales are prepared to elect a Labour government when the conditions are right (although the loss of Labour's 41 Scottish seats, compared to the Tories' one, would certainly make the task harder).

Salmond's wider contention is that his pursuit of progressive policies (such as investment in early years education, higher social security spending, and nuclear disarmament) in an independent Scotland would encourage their adoption in the rest of the UK. But its appeal is diluted by one central fact: there is a better-than-average chance that the next UK general election will result in the formation of a radical Labour government. As leader of the party, Ed Miliband (who will address the Scottish Labour conference on Friday 21 March) has adopted precisely the kind of centre-left policies championed by Salmond. He has pledged to scrap the bedroom tax (which, like the Poll Tax, has become a symbol of Conservative callousness in Scotland), to reverse the privatisation of the NHS, to invest more in early-years education and childcare, to reintroduce the 50p tax rate, to spread the use of the living wage, to rebalance the economy and to increase infrastructure spending. He has condemned the invasion of Iraq (which so alienated progressives in Scotland and elsewhere), prevented a rush to war in Syria and pledged to pursue a foreign policy based on "values, not alliances". Finally, he has denounced the rise in income inequality (which, as Salmond rightly laments, has made the UK one of "the most unequal societies in the developed world"), and has made its reversal his defining mission. If the UK elects a Labour government next May, it won't need Scotland to serve as a "progressive beacon". Rather, it will become a more progressive country through its own means.

In other respects, Salmond's claim that Scotland would help pull the rest of UK to the left is risible. While Labour has pledged to increase corporation tax from 20 per cent to 21 per cent in order to fund a reduction in business rates for small firms, the SNP has vowed to reduce it to 3 per cent below the British level. Rather than a progressive race to top, Salmond would fire the starting gun on a race to bottom. The unflattering comparisons do not end here for the First Minister. As James Maxwell, an SNP supporter, has written on The Staggers, "When Miliband challenged Rupert Murdoch's reactionary influence over British media and political life, Salmond remained strangely loyal to the News Corporation chairman. When Miliband attacked corporate tax avoidance, Salmond handed Amazon £10m worth of Scottish government money and encouraged the company to establish distribution centres in Scotland. Where Miliband has pledged to rein in monopolistic energy companies, Salmond opposed George Osborne's windfall tax on North Sea oil profits. Since becoming leader, Miliband has displayed a willingness to confront 'vested interests' generally lacking in the Scottish First Minister."

One of the few factors that could aid Salmond's flagging cause (the latest poll puts support for independence at just 32 per cent with 57 per cent opposed) is a Tory recovery. With just one Conservative MP in, the fear of another five years under the Tory yoke, and a government wedded to permanent austerity, could help to push many towards separation. By the same measure, then, Labour's consistent poll lead (which stands at nine points today), and Miliband's progressive promise, is one of the forces helping to drive them away.