LONDON: The leader of Britain’s main opposition party on Monday vowed to crack down on employers who pay migrant workers less than Britons in a speech toughening up his immigration policy before next year’s general election.

Ed Miliband vowed that a future Labour government would protect lower paid British workers from being undercut by unscrupulous employers by making this a criminal offense, as well as strengthening border controls.

“When people can be exploited for low wages or endangered at work, it drags the whole system down, undercutting the pay and conditions of local workers,” he said during a speech in Great Yarmouth, eastern England.

“We must end the epidemic of exploitation. We must stop people’s living standards being undermined by scandalous undercutting.”

Immigration is expected to be a hotly debated issue at the election in May as the main parties fight to stem the flow of voters to the UK Independence Party (UKIP), which advocates a hard-line stance.

The latest YouGov poll published in this week’s Sunday Times put Miliband’s Labour neck-and-neck with Prime Minister David Cameron’s Conservatives on 32 percent, with UKIP on 16 percent.

Labour members canvassing on the doorstep are being advised not to bring up the issue of immigration due to fears it could lose them support, according to a leaked party document published in Monday’s Daily Telegraph.