After former Tories Douglas Carswell and Mark Reckless defected, a Labour defection would be a huge boost for the eurosceptic party, which is fighting to convince alienated Labour voters and defy commentators who say it largely draws support from ex-Tories.
Simon Danczuk, the outspoken Rochdale MP who has previously said Ed Miliband's leadership had been suicidal, was photographed by The Sun (£) drinking with Farage in a pub near Tower Bridge.
Danczuk, 48, is defending a majority of just 889 and has been an outspoken advocate for child abuse victims, after his constituency was rocked by a grooming scandal.
Labour has long been accused of underestimating the threat Ukip poses to it.
In October, Ukip were just 617 votes behind Labour in the Heywood and Middleton by-election, prompting Farage to claim they were "ripping lumps" out of Labour in their own heartland.
After Ukip polled first in May's European elections, senior Labour insiders told HuffPost UK's Mehdi Hasan that the scale of the "nightmare facing Labour is extraordinary".
But Danczuk told the tabloid there was "no chance" he would join Ukip, saying: "Nigel and I met for a few pints to talk about politics. We had a very detailed conversation about a whole range of things — Europe and immigration through to the general election and beyond.”
Farage refused to discuss whether he had asked Danczuk to defect but told the paper: "“I meet all sorts of people in politics. I was particularly pleased to meet Simon Danczuk.
“He is an interesting politician who thinks for himself. And he ‘gets’ why Ukip is doing so well in the North of England.”