A sharp fall in EU migration should be a "red line" for the UK in Brexit trade negotiations, according to a campaign group.
Migration Watch UK argues in a new report that the Government must firmly oppose any attempt to seek concessions on immigration as part of the talks.
The paper says it is normal in trade agreements to allow the movement of staff essential for facilitating the flow of goods and services.
But, according to the report, the EU has not previously insisted upon "liberalised" border regimes or freedom of movement as a condition of a trade agreement.
It concludes: "If they were to do so in the negotiations that are pending with the UK it would clearly be driven by political, rather than economic, considerations.
"The UK Government must maintain distinct separation between its trade negotiations and establishing a post-Brexit immigration policy."
Lord Green of Deddington, chairman of Migration Watch UK, said: "A sharp reduction in immigration from the EU must be a red line in these negotiations, not a bargaining chip.
"The Government has already caved in on rights for those arriving in the implementation period.
"They must not capitulate on longer term immigration arrangements.
"That would be a betrayal of the 17 million who voted for Brexit."
Official figures have shown falls in net migration from the EU since the referendum.
An estimated 90,000 more long-term EU migrants arrived in Britain than left in the 12 months to September 2017.
It was the first time net migration from the bloc had dipped below 100,00 since the year to March 2013, and the lowest figure recorded since 2012.
A Government spokesman said: "The Prime Minister has been clear that free movement will end and we will retake control of the UK's borders.
"After we have left the EU, we will put in place an immigration system that works for the whole of the UK."