David Cameron's major policy speech on immigration was overshadowed after official figures showed that the prime minister's net migration target of "tens of thousands" had moved an order of magnitude out of reach.

The Office for National Statistics (ONS) revealed that net migration had surged to 318,000 in 2014, up from 209,000 in 2013 and triple Cameron's less than 100,000 pre-election pledge.

The research body also said there was a "statistically significant" hike in the number of immigrants from the EU as 641,000 people from the union travelled to the UK in 2014, up from 526,000 in 2013.

The data provided a pre-speech dent for Cameron before he unveiled the government's new "crackdown" on "illegal" immigrants.

The Conservatives' plan to present "Britain a less attractive place to come and work illegally" by making "illegal working" a criminal offence in its own right. The prime minister explained the move would enable the government to seize the wages of the "illegal immigrants" and subsequently deter them and their employers.

"The truth is it has been too easy to work illegally and employ illegal workers here. So we'll take a radical step – we'll make illegal working a criminal offence in its own right. That means wages paid to illegal migrants will be seized as proceeds of crime," Cameron said.

The government will also tell more businesses when their workers' visas expire, the prime minister revealed.

But the proposal, by definition, will do nothing to stop the UK's net migration levels rising. The ONS do not attempt to count the number of "illegal" immigrants in Britain for obvious reasons.

The new measures, therefore, would do little to alleviate the pressure on Cameron to meet his manifesto's immigration pledge.

The contentious issue is also likely to be a focal point ahead of planned in/out referendum on the UK's membership of the EU.

Cameron, who is expected to campaign for an "in" vote, made the major constitutional pledge after being pushed in the polls by Ukip and facing discontent on the issue in the House of Commons from some of his backbenchers.

Nigel Farage's party have since billed themselves as a Eurosceptic and anti-mass immigration party. The move paid dividends at the general election when the purple outfit won almost four million votes and secured an electoral foothold in the north of England.

But Ukip were only able to secure one seat in the Commons after Douglas Carswell was re-elected as the MP for Clacton. The party also suffered in-fighting after Ukip's national committee reportedly refused to accept Farage's resignation.

However, Farage has claimed that the party is now "unified" ahead of the historic EU vote, which Cameron has promised to hold by the end of 2017.

Cameron has promised to renegotiate powers around immigration with Brussels as the referendum looms. But the EU is not expected to budge too far because "free movement" is a fundamental principle of the 28-member bloc.

The prime minister even resorted to taking a swipe at the Liberal Democrats, his former coalition bedfellows, when he suggested that Vince Cable countered plans to combat rising immigration levels when in office.

"In the last government the Home Secretary was very keen on controlling immigration, I was very keen on controlling immigration, but sometimes when we got to the Department for Business we got a rather unwelcome response," Cameron reportedly claimed.