THE Conservatives were "catastrophically wrong" in predicting how many North-East seats would turn blue in last year’s General Election, data revealed in a new book shows.

The confidential information, prepared the week before the June 2017 election, suggested the Conservatives were on course to win 371 seats, with Labour expected to slump to just 207 MPs.

The data shows the Tories expected to hold on to Stockton South, where James Wharton was the standing MP, and were expecting to gain Labour seats in Bishop Auckland, Sedgefield, Durham North West and Hartlepool.

The scale of the party’s misguided forecast has been revealed in internal data published in a new book on the election called The British General Election of 2017.

The data shows the Tories underestimated the Labour vote by 15 per cent in Stockton South, 11 per cent in Durham North West, ten per cent in Sedgefield and Hartlepool, and eight per cent in Bishop Auckland.

The book found the modelling, done by ex-US president Barack Obama’s former adviser Jim Messina, was “spectacularly wide of the mark”.

The snap election, called by Mrs May to capitalise on soaring opinion poll leads and the desire to secure a majority to get her Brexit plans through the Commons, resulted in a hung Parliament with just 317 Tories securing a place at Westminster.

The book’s co-author, Professor Philip Cowley, of Queen Mary University of London, said: “This isn’t, as far as we know, the very last bit of modelling they did, but it’s near enough to the election to be a decent sign of how catastrophically wrong their targeting was, and it’s the only bit that’s been made public.

“It shows just how misguided the Conservative campaign was in much of the country - and how they were putting resources into seats they ended up being miles from winning, while thinking they were safe in seats they ended up losing.

“The scale of some of the errors are just astonishing and shows how ill-informed the party’s field campaign was.

Helen Goodman, Bishop Auckland MP, said: “When the Conservative candidate came to the count he thought he’d won.

“What sealed it was Boris Johnson’s disastrous visit to Shildon two days earlier, when he refused to face the crowd and Tory minders insulted our voters.”

Mike Hill, Hartlepool MP, added: “The Tories were overconfident and they thought they would take votes away from Ukip.

“A lot of voters came back to Labour because we focused on the things that mattered to the people of Hartlepool, such as unemployment and the state of the roads, rather than just the EU.”

Dr Paul Williams, MP for Stockton South, said: ‘It is an absolute privilege to be the MP for Stockton South.

“I ran a positive, honest and visible campaign, reaching out to all people in the constituency.”