David Cameron's pledge to bring net migration down to the "tens of thousands" is effectively "dead and buried" as official figures revealed that its level rose to 260,000 in the year to June.
The new Office of National Statistics figures come after home secretary Theresa May warned that ministers were "unlikely" to meet their target for reducing net migration - the difference between those arriving and leaving - to below 100,000.
Some 583,000 people immigrated to the UK in the year ending June, the Office of National Statistics (ONS) said, a "statistically significant increase" from the 502,000 in the previous 12 months.
The rise was driven by increases in immigration from the European Union, which was up 45,000 and outside the EU, which was up 30,000, it said.
Deputy Prime Minister Nick Clegg said the Tories' failure to meet their target for reducing net migration - which the Liberal Democrats have always opposed in government - would undermine public confidence in the immigration system.
"This was a Conservative preoccupation. They made that promise. They have now broken that promise and they will have to suffer the embarrassment of having done so," he said on his weekly LBC radio phone-in.
"I think that it does damage public confidence in the immigration system by over-promising and under-delivering in this way."
Another "statistically significant increase" in Romanian and Bulgarian citizens arriving in the UK was flagged by statisticians in the period, rising to 32,000 from 18,000 in the previous year.
Romanian citizens had the highest number of National Insurance number registrations in the year to September - 104,000 - followed by Polish citizens at 98,000, the ONS said.
Total National Insurance number registrations to foreign nationals increased by 12% to 668,000 in the same period, the figures showed.
A rise in immigration from outside the EU, up 30,000 to 272,000, was in part driven by an increase in family and friends arriving to join others, the ONS said, which was up 19,000 to 54,000.
Dr Carlos Vargas-Silva, acting director of the Migration Observatory at the University of Oxford, said: "The Government's own data showed in 2011 that their policies were not expected to reduce immigration by enough to hit the target.
"So we have been watching a result that we have expected for three years unfold in slow motion.
"Increased EU net migration has certainly meant that the degree by which the target is missed will be much higher, but it is clear that the target would have been missed with or without this increase, as non-EU net migration alone is way over 100,000."
Former Labour immigration minister Barbara Roche, chair of the cross-party Migration Matters Trust, said the latest migration figures showed that parties must "promise what you can deliver and deliver what you promise".
"The public is already cynical about the mainstream parties’ policies on immigration and committing to unachievable targets makes matters worse," she added. "It’s time to be straight with the public on two counts."
"First, if you believe we should stay in the EU, then freedom of movement is here to stay, which means immigration is likely to rise as our economy does well compared to the rest of the EU.
"Second, and this is the real taboo, this migration is overwhelmingly good for Britain, plugging skills gaps, boosting output and bolstering our recovery.
"Only when the parties are honest about these two issues will we finally approach a serious debate on migration.”
Sunder Katwala, director of British Future, said: "The net migration target is dead and buried. The question is what happens next, why this has happened and what the Government is going to do about it."