Polling stations open for crucial byelection, which could result in Ukip gaining its second MP • Live updates from the Rochester and Strood byelection

Voters have begun to go to the polls in the crucial Rochester and Strood byelection that is widely expected to deliver Ukip its second MP.

Polling stations opened at 7am in the north Kent town, with the frontrunners Ukip and the Conservatives mounting a huge operation to get their voters to cast their ballots.

Opinion surveys conducted in the runup to election day suggest the clear favourite is Mark Reckless, the area’s former Tory MP whose defection to Ukip triggered the contest. On Wednesday night, he heaped pressure on his former bosses in the Conservative party by claiming there were two more Tory MPs considering jumping ship to Nigel Farage’s party if it wins in Rochester.

Further defections would be likely to prompt a crisis in Downing Street about the haemorrhaging of the Tory vote six months before the general election, and potentially a move on David Cameron’s leadership.

Reckless said: “During the campaign I have spoken with two Conservative MPs about the possibility of their moving over and I think they will want to see what the result is before making any decisions. One of them I had discussions with by telephone and the other I met in an undisclosed location, not in the constituency. It is a very individual decision. And I feed back to Nigel [Farage] on those conversations.”

Eric Pickles, the Conservative communities secretary, said on Wednesday he was certain his party could win in defiance of the polls over the past few weeks, and dismissed the idea of more defections.

Campaigning outside Rochester town centre, he said: “I don’t think there will be any [defections]. We have brought the economy back from the brink … At times when we talk to our friends in Ukip it sounds as though the only thing they really like about our country is its past.”

Reckless’s comments are likely to provoke strong speculation about possible candidates for joining Ukip.

One of the favourites is Peter Bone, the Eurosceptic Conservative MP for Wellingborough, who is speaking in a debate on Thursday in Cambridge in favour of the motion that Ukip has been good for British politics.

Asked whether he was about to defect, Bone did not deny it, although he called for Ukip members to reunite with the Conservatives on the centre-right. “You’ve seen what the motion says,” he said. “It’s quite clear. It says Ukip is a good thing for British politics, which in my view it is to have another party which is pushing the Europe debate on and about immigration. It’s helped moved it along.

“My view is that Ukip membership should come back and join the Conservatives and be part of a centre-right majority in this country.”

Other possibles are John Baron, the MP for Basildon and Billericay, who has said “never say never” to the prospect of defection. He was treated with kid gloves in the House of Commons by the prime minister on Wednesday as he asked an awkward question about what the government was doing about nuclear test veterans.

Conservative paranoia about defections was also fuelled when a picture emerged of Mark Pritchard, the party’s MP for The Wrekin, photographed smiling next to Farage at an event.

The Tory rejected the idea he was about to join Ukip, telling the International Business Times that it was just a “friendly photo, not a sign of any political allegiance”.

A victory for Ukip will be particularly embarrassing for Cameron because of his promise to throw the kitchen sink at the seat.

If returned, Reckless will be Farage’s second MP, after Douglas Carswell defected from the Conservatives and then won back the seat for Ukip in the Essex seaside town of Clacton.

As the campaign entered its final day, it descended into acrimony over the issue of immigration, with Ukip’s candidate accused by Labour of endorsing the idea of repatriation for some EU immigrants.

Speaking in an ITV hustings, Reckless suggested that some European migrants, such as a Polish plumber, should only be allowed to stay for a fixed period on a work visa if the UK left the EU as advocated by his party.

Yvette Cooper, the shadow home secretary said: “To hear the language of repatriation coming from someone they [Ukip] hope will be their second MP is shameful.

“It’s a policy that comes straight out of the last BNP manifesto and does not reflect British values.”

Ukip was forced to clarify that it is in favour of allowing all existing EU migrants to stay, suggesting Reckless had misunderstood the question. The Ukip candidate then went on to infuriate the Conservatives by accusing them of being the ones who were conducting a “BNP-light” style campaign.

The Tories have been campaigning particularly hard on the issue of immigration, with their candidate, Kelly Tolhurst, saying she wanted Cameron to take more action.

In a sign of her party’s fears about seeming too soft on immigration, Tolhurst refused to condemn the idea of EU migrants being asked to leave the country, simply criticising Reckless for changing his mind about his views.

She also distributed a letter, which does not mention the Conservatives, that juxtaposed a statement about reducing immigration and a line about people not feeling safe on the streets.

Tolhurst said she was still hopeful of winning, but was reduced to begging for votes from supporters of other parties in an attempt to keep Ukip out of the constituency.

“It’s a two-horse race and the reality of it is if we don’t want to wake up to a Ukip MP on Friday 21 November then people who would normally be voting for Labour, the Lib Dems or anyone else, then they need to be voting for me,” she said.

In contrast, Ukip was in victory mode, with dozens of its staff, politicians and activists gathering for a lap of the town in a party-branded bus.