Alec Douglas-Home’s 1963 cabinet was composed of 24 ministers. Among them were 11 old Etonians, six hereditary peers, two of Winston Churchill’s sons-in-law, and the editor of the Daily Telegraph. All of them were men. And yet, for all its starchy homogeneity, this cabinet was the last time the ministers of the British government equally represented the northern and southern halves of England.

For the latest edition of Spotlight – found in this week’s New Statesman – we looked at the composition of every senior government for the last century and found that Theresa May’s 2017 cabinet has a higher proportion of MPs with constituencies in the south of England than any other since at least 1900.

Of the 20 cabinet ministers in May’s government that have constituencies in England, just three have seats north of Birmingham; 85 per cent are elected in the south.

We defined “southern” cabinet ministers as those who are MPs with constituencies south of Birmingham (our definition of “northern” cabinet ministers therefore includes many constituencies in the Midlands – we are talking about the northern half of England rather than the less well-defined “the north”).

We drew this imaginary line because, according to recent ONS data, it very roughly divides the population of England into two groups of around 25 million people. Having looked at the composition of every cabinet since 1900 on these criteria, we found no government that was more skewed towards the lower half of the country than the current May ministry.

This disparity has grown over the past 50 years. Churchill’s cabinet was 54 per cent southern; Eden’s was 56 per cent southern. Edward Heath’s cabinet rose to 59 per cent. But it was with the formation of Margaret Thatcher’s 1979 cabinet, in which 81 per cent of the English MPs were from the south, that the trend cemented itself. For the past 30 years, no Conservative cabinet (or the 2010 coalition) has drawn any less than 70 per cent of its ministers from below the Birmingham line.

Northern politicians to whom we’ve shown these figures say it confirms the sense that the country is governed by, and for, the south of England. Steve Rotheram, Liverpool’s metro mayor, told us: “Maybe there is a tendency to dismiss complaints from Northern politicians about southern bias, but my experience in Westminster convinced me that metro-centricity and southern bias are hardwired into government thinking and Whitehall control.

“The balance of the current government only exacerbates a gulf in comprehension and knowledge that continues to disadvantage the North and makes a mockery of their rhetoric on economic re-balancing.”

Partly, of course, this disparity simply illustrates where the safe seats lie, in a country in which voting has for many generations been largely a question of left or right. Labour governments tend to mirror the trend, with cabinets that are taken mostly from northern seats. But with Conservative governments in power for the majority (60 per cent) of the years since 1945, it is true that most of the big decisions made by senior governments in modern political history have been made by cabinet ministers who live in, and are elected by, constituencies in the south of England.

Rotheram says this is reflected in policy today. “The interests of the north can only be adequately represented around the cabinet table by ministers who understand, have experienced and ideally represent northern communities. An absolute commitment to fund Crossrail for the north would be a good start. For every £1 we get here in transport funding, the south gets £6. More northern voices would surely improve our chances of fair treatment. I think the current government sees the north as a far-flung province, or some kind of latter-day colonial territory.”

Devolution should help to regulate the north-south swing of central government. But while metro mayors such as Rotheram have new powers and control over budgets, decisions on the huge transport projects needed to link cities and create a “Northern Powerhouse” or a “Midlands Engine” are made by cabinet ministers such as Philip Hammond and Chris Grayling – both of whom ask the people of Surrey for their seats in parliament.

Theresa May travelled to Teesside last month to claim that “we have made good progress on this [the Northern Powerhouse] agenda”, and to reassure northern voters that a balanced economy remains a priority for the Conservatives. It remains to be seen how much will be invested in this promise by a cabinet that has so little electoral interest in fulfilling it.

Read an in-depth interview with Steve Rotheram here