Ministers are drawing up plans for a post-Brexit immigration policy which would see just 40,000 fewer EU migrants a year come to UK, a leaked impact assessment suggests.

The Telegraph can disclose the economic analysis, drawn up with the support of Amber Rudd, the Home Secretary, suggests that EU workers will be given "preferential" treatment if Britain secures a free trade deal.

Under a "flexible migration" scenario, described as a "midway point between strict policy and continued Labour mobility", EU workers would have to earn £20,500 to come to the UK. More than 230,000 EU migrants currently come to the UK every year.

The analysis suggests that migration controls will be far tougher if Britain leaves the EU without a deal, leading to 90,000 fewer EU workers a year.

It states that if the EU leaves without a deal, migrants would be required to have degrees, a job offer and earn at least £30,000, bringing them into line with visa requirements for non-EU workers.