Party points to OBR statistics which show negative economic effect of ending free movement
Lucas wants Britain to retain free movement, and remain a member of the Single Market
The Green Party will today launch a staunch defence of free movement. Speaking in Sheffield  the party's co-leader Caroline Lucas and former leader, Natalie Bennett will defend migrants' contribution to Britain and pledge their support for continued free movement within Europe.
Caroline Lucas, who was one of few politicians to stand up for free movement in the EU Referendum, will say that migration has 'enriched' Britain both culturally and economically. She will slam the other parties for 'failing to make the case for free movement' and accuse the Tories of 'facilitating a race to the bottom on migration' and 'sacrificing our economy on the altar of ending free movement'.
She will point to figures from the Office of Budget responsibility which show that cutting migration to 185,000 (well above the Tories' target) will cost the treasury up to £6bn.
A recent study by the London School of Economics has blown apart a number of key myths around migration, saying: "Immigrants pay more in taxes than they take out in welfare and use of public services. UK-born individuals, on average, take out more in welfare and benefits than they pay in taxes. So immigrants help to reduce the budget deficit. There is little evidence that immigrants have negative effects on crime, education, health or social housing."
Caroline Lucas is expected to say:
"The Green Party is proud to celebrate free movement and the huge contribution that migrants have made to Britain. It's easy to blame immigration for the lack of school places or GPs but it's also wrong. Free movement has hugely benefited our economy and made our communities richer. The challenge is to ensure we all share those benefits more fairly and equally.
"Free movement 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.
"The economic arguments for free movement are strong too. 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 free movement, 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."
Natalie Bennett, who is herself a migrant from Australia, will say:
"Britain's political culture is awash with migrant-blaming rhetoric. As someone who came to this country from abroad, and is now proud to call it my home, I find it particularly disturbing to see politicians continuing to blame all of this country's problems on migration. We know that cuts to schools, our hospitals in crisis and the housing shortage are the fault of failed government policies, not migrants. Migrants may be a convenient scapegoat for those in power, but the truth is that people coming to Britain from abroad make a huge contribution to our economy and our society."
 The event will take place at 10am on Friday 2 June 2017 at Broomhall Centre, Broomspring Lane, Broomhall, Sheffield, S10 2FD