Liberal Democrat leader Nick Clegg has challenged Conservative leader David Cameron on his party's policy of immigration level 'caps', during the prime ministerial debates.

He asked David Cameron to give a "number" for the kind of caps that would be put in place.

The Conservative leader said the figure would be set in consultation with experts like business leaders.

Both Cameron and Brown challenged the Lib Dem's position of holding an amnesty for existing illegal immigrants.

The exchange came as a result of a question from the floor, asking how to make immigration fairer.