Tory plans to cut net migration to 100,000 could cost the Treasury billions, according to the Greens.
Co-leader Caroline Lucas will make a speech defending free movement on Friday, alongside former party leader Natalie Bennett, who is standing as a candidate in Sheffield Central.
She will accuse the Tories of ‘facilitating a race to the bottom’ on immigration, after Theresa May confirmed she would be sticking with her target of cutting net migration to below 100,000.
“It’s easy to blame immigration for the lack of school places or GPs but it’s also wrong,” Lucas will say.
“Freemovement enriches and diversifies our communities. A culture that’s rich in diversity is exposed to new ways of thinking, new ideas, new languages and new opportunities. It is outward thinking, rather than self-limiting.”
Both Labour and the Conservatives have said Brexit will mean an end to free movement, with the Tories committing to reducing net migration in their manifesto and Labour promising ‘a fair, managed system’.
Office of Budget Responsibility figures show cutting migration to 185,000 - still well above the Tory target - could cost the Treasury as much as £6bn.
Throughout the election campaign, experts have warned about the potential impact of drastically cutting migration levels.
The NHS could be left with a bill of half a billion if aging British expats return home after Brexit and the healthcare, construction and agriculture sectors could face severe staff shortages if they lose EU workers.
Lucas will say: “We’d be a poorer country without the taxes EU nationals pay, and the work they do in our hospitals, care homes and councils. Without freemovement, there is a very real risk that the economy will not be able to generate enough tax take to support current levels of investment in the NHS or other public services – levels which have already been cut to the bone.”