Now, after delays and inflation fuelled by Brexit, COVID and the invasion of Ukraine, this figure is closer to £100bn. Prime Minister Rishi Sunak has also avoided answering questions on whether the Birmingham to Manchester leg of the route will go ahead, leaving the future of the project shrouded in uncertainty.

So why was the initial cost estimate so different to what the final number will be?

On the Sky News Daily, Niall Paterson sits down with our business correspondent Paul Kelso to discuss the problems with the way the UK plans major infrastructure projects and asks whether any of these projects ever come close to what they are predicted to cost.

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