Britain wants to change the rules governing the free movement of people across the EU, Home Secretary Theresa May will tell European ministers, BBC reported.Mrs May will speak in Brussels, ahead of the lifting of movement controls on Bulgarians and Romanians.She says free access to Labour markets must not be allowed to lead to "mass migration".However, some other countries have already vowed to defend what they regard as a fundamental EU principle.EU justice and home affairs ministers will met in Brussels on Thursday.'Mass migration'Mrs May argues that problems caused by free movement must be addressed and the rules should be changed.In a statement she questioned why national governments should not be be allowed to impose a cap on numbers if European immigration reached certain thresholds.She said she planned to make clear at the Brussels meeting "that I believe we need to change the way free movement rules work."First, for future accession treaties, we must be able to slow full access to each other's labour markets until we can be sure it will not lead to mass migration."Second, looking ahead, we must seize the opportunity presented by the prime minister's plan to reform the EU and address the problems caused by free movement."It is right that the national governments of the EU reform the way free movement rules work."Welfare systemsThe debate is taking place in advance of the lifting of transitional controls on Romanians and Bulgarians - from 1 January there will be no restrictions on them working anywhere in the EU.BBC Europe correspondent Chris Morris, in Brussels, said there was sympathy for Britain's demand that abuse of welfare systems should not be permitted - because other countries shared the same concern.But there was little support at a political level for a fundamental reassessment of the idea of free movement, our correspondent added.One diplomat from an eastern European member state said no one would accept some countries being treated as second class EU citizens because a free market in goods and services also has to be a free market for labour.Mr Cameron has suggested that citizens from other EU countries would not be able to claim out-of-work benefits for the first three months in the UK and would not be able to extend claims beyond six months if they had no genuine prospect of work.Laszlo Andor, a European commissioner, angered Mr Cameron by commenting that the UK was at risk of becoming a "nasty" country if it curbed benefits and sought to limit freedom of movement by EU nationals.ANN.Az