BBC Question Time host Fiona Bruce could not hide her bewilderment last night when a Tory MP tried to take credit for some of Labour’s new infrastructure plans.

The government has just unveiled a series of building projects meant to boost economic growth in the coming years, including expanding Heathrow Airport to include a third runway.

However, shadow minister Dr Kieran Mullan claimed many of the new ideas had been copied from the previous Tory government.

Amid a wider conversation about Labour’s Heathrow plans, Bruce said to Mullan: “This is something that the Conservatives support, building a third runway... [but you] didn’t do it of course! But you support it.”

Mullan replied: “When it was before parliament last time we supported it. 

“But I have to say, I think yesterday was pretty desperate stuff from the Labour Party.

“They announced what they said was a whole new set of projects that were all designed to implement growth, except it turned out most of them weren’t new and they weren’t the Labour Party’s ideas.”

Bruce looked at him with incredulity, and asked: “What? They were your ideas, the Conservative Party’s ideas? So why didn’t you do them then?”

A flurry of laughter broke out among the audience at that, but he pushed on: “Some of them are completing this year that we started!”

“What, sorry, nine new reservoirs?” Bruce asked.

He replied: “Some of them, some of them! Some of the projects are not new and are not the Labour Party’s ideas.”

He did not explain which projects he meant.

The Tory MP then went on to claim the main growth problem facing the government is “a short-term economy”.

He said Labour had inherited the fastest growing economy in the G7 from the Conservative Party, but “they’ve turned that into an absolute hard stop”.

The shadow minister said: “We’ve gone from the fastest growing economy in G7 to zero growth in the economy.”

Bruce said: “In that final quarter?”

But he said it was actually across the whole of the Tory government from 2010.

The UK’s trend rate of economic growth declined after the 2008 financial crash, and the British economy suffered historically weak growth over the 14 years of Tory rule.

The National Institute of Economic and Social Research found the UK’s trend annual growth rate declined from 3.4% a year between the postwar period and 1973, reaching 2.3%on average until 2008 before falling to 1.2% in the years afterwards.