A predicted fall in asylum applications to be announced this week may be masking an increase in illegal immigration, it has been claimed.

The warning comes as the government prepares to announce that it is winning the war against asylum abuse.

Figures for the three months to June may reveal that ministers have met the prime minister's pledge to half the number of asylum applications.

But ministers are today warned that the much publicised crackdown on asylum abuse may be resulting in record numbers of illegal entrants.

Keith Best, the chief executive of the Immigration Advisory Service, said: "The figures will have come down substantially but the trouble is that it is almost certainly going to be at the expense of greater illegal immigration.

"The benefit for David Blunkett is that nobody can say for sure that his legislation has led to this side effect because illegal immigration cannot be quantified.''

Recent legislation which denies asylum seekers support if they fail to make an immediate claim has removed the incentive to make a formal application.

"You may as well stay here clandestinely and hope that you'll be able to remain undetected for 14 years - after which time you can come clean and claim indefinite leave to remain,'' he said.

A spokesman for the Home Office denied that illegal immigration was risisng as a result of the government's crackdown.

"What disproves this is that new equipment at Calais and Coquelles is picking up clandestines before they come to Britain," the spokesman told the Press Association.

"Critics cannot point to any evidence that illegal immigration has got worse while asylum applications have improved.

"Shortly we will have full juxtaposed controls with the French so that we have effectively moved our border over there.

"If we want to have a full impact on the black economy we should have identity cards as the rest of the developed world does - and that is still our view.''