A former Conservative frontbencher has warned David Cameron that proposals to limit EU immigrants' access to benefits could be discriminatory.

Reports at the weekend suggested Downing Street was considering the ideas, put forward by the think tank Open Europe. They include limiting the in-work welfare payments, such as tax credits, that migrants can receive.

But Dominic Grieve, the former attorney general, warned: "The difficulty with this proposal is I think it's discriminatory".

David Cameron is expected to set out his plans on immigration in a major speech potentially as early as this week. The Prime Minister is under intense pressure on the issue.

New figures released later this week are expected to show the Conservatives have missed their pledge to cut net migration to the tens of thousands. Yesterday another former frontbencher, Owen Paterson, called on Mr Cameron to apply to leave the EU immediately after the next general election.

Mr Paterson, the former Environment Secretary, warned that the process would take two years, during which the EU would be forced to reform to prevent a UK exit.