Despite the controversy, which the Ukip leader dismissed as a "minor cause for confusion", the Tories appear to have resigned themselves to losing the Kent seat in today's poll. The bookies put the Conservative defector odds-on to win.

Yet, privately, Labour is just as worried about the impact Ukip could have on its chances at the General Election, particularly in northern English seats.

This week, it pushed out not one but two keynote pledges on immigration; introducing 1,000 more border staff and restricting eligibility of unemployment benefits to EU nationals from three months to two years.

Ed Miliband is hoping his party's vote at Rochester - which until 2005 before boundary changes was a Labour seat - will hold up while Nick Clegg is bracing himself for another Liberal Democrat lost deposit.

Mr Reckless, who had a 10,000 majority as a Tory MP in the Kent seat, sparked controversy after it emerged he told a hustings meeting that EU nationals would probably be granted work permits for a "fixed period" if the UK left the EU.

Asked specifically what he thought should happen to a Polish plumber who lived in the Rochester area and whose children went to school there, the Ukip candidate replied: "In the near term, we'd have to have a transitional period. We should probably allow people who are currently here to have a work permit at least for a fixed period. People, who have been here a long time and integrated in that way, we'd want to look sympathetically at."

l MPs last night approved the controversial European Arrest Warrant in a symbolic vote brought forward by Labour to try to embarrass the UK Government ahead of today's by-election. Some 29 rebels voted against it./Herald Scotland