THERESA MAY leapt aboard a helicopter to jumpstart her election campaign on Wednesday afternoon in Bolton North East and so set a baseline by which we can judge our local seats.

Bolton North East was Conservative until New Labour won it in 1997 with a 12,669 majority. Since then, the majority has eroded away to 4,377, and it is now Mrs May’s 48th most winnable seat. Mrs May would only launch her campaign in a seat she is confident of winning – so what does the Bolton baseline look like when applied over here?

Well, Middlesbrough South and East Cleveland is, unsurprisingly for a historic swing seat, extremely likely to fall to the Tories. It is target number 21, and requires a swing of only 2.48 per cent.

Then comes Darlington, target number 35. It was marginally Conservative in the hands of Michael Fallon until 1992, when Alan Milburn won it. In 1997, Mr Milburn’s majority peaked at 16,025. It has since eroded to the 3,158 Jenny Chapman holds today. It requires a 3.48 per cent swing to the Conservatives and, as it is below the Bolton baseline, it will fall to the Tories on June 8.

Similarly Bishop Auckland, target 46. It has been solidly Labour since Ben Spoor, a Witton Park lad, won it 1918. The only aberration in a century was four years in the early 1930s when a Liberal held it. Labour’s majority peaked in 1997, at 21,064, but has since eroded to the 3,508 Helen Goodman holds today. It requires a 4.45 per cent swing and the Bolton baseline would turn it blue. Extraordinary.

Our other seats are beyond the Bolton baseline: Hartlepool is number 71; Tynemouth is 75th and Sedgefield is 87th.

But, if you believe the polls, the Tories are heading for a 100 seat majority. Currently they have a 13 seat majority which means they will win an extra 87 seats – and Sedgefield would clinch the ton.

That would be stunning, a seachange in local political affairs. Even the Conservatives winning three seats is unprecedented in a generation – but that’s what the Bolton baseline suggests will happen.

SO, lucky people, we are all going to get to vote twice in a month – there are county council elections in Durham and North Yorkshire plus the mayoral election in the Tees Valley on May 4, so no one is going to miss out.

The local results will be pored over like ancient runes to see what they say about the general election a month later – particularly, I think, the mayoral result which if the Tories come close to pipping Labour will offer a clue about the fate of the Darlington and Hartlepool seats in the general election.

But past experience suggests the locals are not reliable predicators. You have to go back to 1983 and 1987 to find similar circumstances, and on both occasions, Margaret Thatcher’s Conservatives won the locals by a few points but swept the national election a month later by double digits.

However, one local result may have triggered our current predicament. On Maundy Thursday, fewer than 1,300 people in Coulby Newham on the edge of Middlesbrough elected a replacement for their retiring Labour councillor. By a slender 33 votes, they chose a young Conservative, Jacob Young. The Tory vote was up 8.3 per cent; Labour was down 8.2 per cent. It was the first time ever Coulby Newham has elected a Conservative; probably the first time in 21 years that the Tories had won a seat from Labour on Middlesbrough council.

It is in Mr Blenkinsop’s 21st target constituency and this seachange result played a part in him standing down. It may even have emboldened Theresa May: if the Conservatives can steal a council seat from Labour in the Boro, they can steal Parliamentary seats anywhere.