LABOUR will eventually back the troubled high-speed rail project, Mr Cameron predicted – or become the party “turning their backs on the North”.

The HS2 scheme was thrown into jeopardy this week, when Shadow Chancellor Ed Balls said he might pull the plug – even if the cost remained below £50bn, including new trains.

But the prime minister said: “I don’t believe Labour will, in the end, go wobbly on it because they will be completely turning their backs on the North of England.

“They will be betraying people in Yorkshire, they will be cementing a position as the party of the past - not the future. So I don’t believe they will do it.”

Mr Cameron also sought to strengthen the case for HS2, which will deliver 225mph trains from London to Birmingham by 2026 – and then a Y-shaped network, on to Leeds and Manchester.

Through trains will cut the Newcastle to London journey time from 2hrs 52mins to just 2hr 18mins – and the Leeds-Birmingham time to 2hr 7mins, from 2hr 52mins.

The prime minister said much more - £37bn – would be spent on other rail projects in the next parliament, than on the start of high-speed rail.

And he said: “The rest of the world is adopting high-speed rail technology, so we should be doing the same “We need a new West Coast line. Do we build an old-style Victorian railway or do we a new high-speed railway? It seems, to me, absolutely right, to choose the high-speed version.”