Control of Britain’s borders is not up for negotiation and will be brought “back here” after the UK leaves the European Union, Brexit Secretary David Davis has promised.

In comments that will be welcomed by Brexit supporters, Mr Davis said that migration levels will be determined “in the national interest” by the government and will not be subject to any promises in return for a better economic deal.

Immigration was one of the biggest issues in Britain’s EU referendum, with many working class Britons saying unlimited EU migration was depriving them of jobs and driving down wages.

Since the vote, however, there have been concerns that a “soft Brexit” will fail to take back control of Britain’s borders, a position seemingly backed by UKIP MP Douglas Carswell.

Despite Mr Davis’s promise, it remains to be seen whether he has enough support within his own party to see it through.

He himself appeared to back a “soft Brexit” earlier this month when he hinted that Britain could still pay into the EU budget, and said that although he would be “ending free movement as it has operated before” he would not “do so in a way that it is contrary to the national and economic interest.”

Other Conservatives have also backed a “soft Brexit”, a position supported by nearly all the opposition parties within the House of Commons.

Also casting doubt on the future of Brexit, Britain’s EU ambassador has claimed Britain’s EU exit could take up to 10 years to finalise and even then could fail.

Sir Ivan Rogers said other EU member states are pessimistic about a deal being reached within two years, although he did say that a final deal would be more likely to be a free trade arrangement rather than continued single market access.

A spokesman for the Prime Minister said: “We don’t recognise this. The Government is fully confident of negotiating a deal to exit the EU that works in the interest of both the UK and the rest of Europe.

“It is wrong to suggest this was advice from our ambassador to the EU. Like all ambassadors, part of his role is to report the views of others.”