Blunkett: I can't defeat people smugglers

David Blunkett today admitted he was virtually powerless against criminals who smuggle thousands of illegal immigrants into Britain every year.

As he launched his latest purge - against bogus students and sham marriages - he confessed to being beset by a huge range of "difficulties".

The Home Secretary told Radio 4's Today programme: "Every time I take a step, the organised criminals behind the exploitation of normal, legitimate routes find a way round it."

Mr Blunkett complained that his liberal critics claimed he was "too tough" and he also derided commentators who claimed Britain's immigration problems could be solved with a single "big bang".

He will make it tougher to get student visas - there are 300,000 at the moment, mostly for people at language schools.

Some studies have put the number abusing the visas - enrolling on bogus courses and then working in Britain illegally - at 15,000.

Mr Blunkett said he thought the total was not that high but said: "It could be just a few thousand ... but a few thousand is enough to undermine public confidence."