Britain will end the free movement of labour immediately after Brexit and introduce measures to drive down the number of lower-skilled EU migrants, a leaked government document published by TheGuardian newspaper said on Tuesday.

Reducing net migration to Britain was one of the main reasons behind last year's vote to leave the European Union, but firms have expressed concern they may not be able to hire the skilled and unskilled workers they need after Brexit.

"Put plainly, this means that, to be considered valuable to the country as a whole, immigration should benefit not just the migrants themselves but also make existing residents better off," TheGuardian quoted the document as saying.

The government envisages a dual system for EU citizens arriving after Brexit, with those wishing to stay long-term needing to apply for a two-year residence permit.

Those deemed "highly-skilled," however, would be allowed to apply for a permit for up to five years under the proposals. 

In the lengthy document, marked "sensitivem" Britain's interior ministry also says it may "tighten up" the definition of family members allowed to accompany EU workers in Britain.

TheGuardian said the document had yet to be endorsed by Prime Minister Theresa May's top team of ministers.

The government does not comment on leaked draft documents, a government spokesperson said.      

"We will be setting out our initial proposals for a new immigration system which takes back control of the UK’s borders later in the Autumn," the spokesperson said.

May has previously said that free movement of labour would have to end when Britain leaves the bloc, but she has so far offered no detail on what kind of immigration system she wants.

The Guardian said the government was also outlining a phased introduction of a new immigration system that ends the right to settle in Britain for most European migrants – and places tough new restrictions on their rights to bring in family members.

"Food and drink manufacturing, Britain's largest manufacturing sector, will be alarmed by the proposals contained in the document published by The Guardian," The Food and Drinks Federation said in a statement.

In August, net migration to Britain fell to its lowest level in three years in the 12 months to the end of March, with more than half the drop caused by EU citizens leaving and fewer arriving since the Brexit vote.

But, at 246,000, the figure is far higher than the "tens of thousands" May has repeatedly stressed she believes is a sustainable level of migration.