Shadow chancellor John McDonnell was unable to say how much the Labour party's spending plans would cost the taxpayers, in terms of servicing the cost of additional borrowing required to fund initiatives ranging from his proposed nationalisation of utilities and rail networks to investment in infrastructure.

In an interview with the BBC on Thursday (23 November), McDonnell was asked eight times what cost the British public should expect in terms of extra spending on servicing government debt, currently at £48bn, should Labour be elected to power.

However, the shadow chancellor failed to come up with a figure and claimed the additional borrowing would "pay for itself."

A flustered McDonnell also quipped: "The type of journalism where you go into an interview when someone asks about a particular figure is a trite form of journalism, that's why we have iPads and advisors."

Without putting a figure, he added that the borrowing would be "minimal" and "rapidly returned" to the taxpayer.

"Economic growth under Labour would see the borrowing pay for itself," he added.

When challenged that every form of borrowing incurs a cost, the shadow chancellor said: "What we would do is ensure that all day to day goverment spending is not paid for by borrowing.

"It will be paid for through our tax system. All our borrowing costs would be rapidly returned to the taxpayers."

On Wednesday, whilst speaking on the BBC's Budget 2017 programme, McDonnell clashed with veteran broadcaster Andrew Neil, after claiming that several asset managers were supportive of the Labour party's plan for nationalisation of key utilities and their holdings to be valued by parliament, as they wanted the "certainty of a government that invests."

When pressed by Neil to name some of the asset managers the Labour party was in talks with, McDonnell said there were a "range of asset managers" whom he refused to name.

After the broadcaster quipped that it was "impossible to check" the shadow chancellor's claim, McDonnell asked "Are you doubting my honesty?"

As co-anchor Simon Jack intervened to say that it was "unusual" for asset managers to have their assets valued by parliament, McDonnell said: "No it isn't, what they are saying to me is that they want a stable government that will invest in infrastructure, and that's what we'll give them."