According to a YouGov poll in today's Sun, 78 per cent of people believe that David Cameron is "unlikely" to deliver his immigration promises. They're right. There is no chance of Cameron meeting his pledge to reduce net migration to "tens of thousands" a year by the end of this parliament.

As I reported last month, net migration to Britain rose by 21 per cent to 239,000 last year (see graph). The problem for Cameron is that the rise was driven by two trends - a fall in emigration and a rise in EU immigration - over which he has no control. One of the PM's biggest errors was to set a net migration target - the difference between the number of people entering and leaving Britian - as opposed to an immigration target.

Had Cameron merely promised to reduce immigration he would have had a good chance of succeeding. Contrary to the claims of the right-wing press, immigration has barely risen since 2004. Instead, by adopting an unachievable target, he set himself up for failure.