Election 2017: Michael Fallon admits Tories do not know the cost of their immigration plans

Sir Michael Fallon has admitted the Conservatives have not costed out one of their key manifesto promises aimed at reducing immigration by two-thirds.

The Defence Secretary was forced to admit that they did not know how much a proposal to double the Immigration Skills Charge - a levy imposed on organisations for every skilled non-EU worker they hire - would cost the economy.

The proposal is one of a range of measures proposals by the party aimed at of reducing annual migration to the "tens of thousands" - a promise originally made in their 2010 manifesto.

The aim of the Immigration Skills Charge is to force business owners to train up UK workers instead of recruiting the skills they need from abroad.

But critics, including members of the party itself, have criticised the plans. Former small business minister Anna Soubry called it “a tax on successful business”.

Sir Michael claimed the idea reflected the party’s “ambition” to cut down on immigration rather than a specific, mapped out plan, when asked about the proposal on the BBC's Newsnight.

“We haven’t set out a formulation of how much it will reduce by each year, what we’ve set out is our ambition to continue to bear down on immigration," he said. “There has been various academic work done on the cost of immigration."

He added: “We’ve made it clear that we accept there is a cost and we want to make sure that British companies do contribute to the training of British workers when they want to fill that post”.

It follows a similar mishap by former Education Secretary Michael Gove who mixed up several figures on immigration during an interview with Nick Ferrari on LBC.

Mr Gove misstated how large the skills charge was, suggesting it was going up from £2,000 per worker per year to £4,000 per worker per year instead of an increase from £1,000 to £2,000.

He then significantly overstated the number of non-EU workers arriving in the UK annually.