Labour's candidate for the Oldham West and Royton by-election will be standing for "a divided party", Ukip leader Nigel Farage has said.
On a visit to the constituency ahead of next month's vote, Mr Farage said Jim McMahon would be "very much at odds" with Labour leader Jeremy Corbyn.
He said: "It is looking like they have picked a Blairite in a Corbyn-led party.
"He is a good candidate but he is standing for a divided party and he is not standing for local politics in Oldham - he is standing for Westminster.
"There are shades of the 1980s about all of this when, one constituency to the next, Labour had completely different representatives.
"He clearly would be very much at odds with Corbyn over many, many things."
He said Ukip's candidate, John Bickley, would not need to argue with Labour as he predicted "they will argue amongst themselves".
Mr Farage continued: "John did say that he (Mr McMahon) would be a very good candidate and they probably would select him, and they have.
"And that is, from their perspective, the right thing to have done, but that does not take away from the fact you have got a Labour Party that has a cultural civil war going on between two different wings of it."
Labour council leader Mr McMahon saw off the challenge from more left-wing rivals, including a former MP and ally of Mr Corbyn, to contest the seat triggered by the death of Michael Meacher, who represented Oldham in the Commons for 45 years.
Among rivals he defeated were former MP Chris Williamson, a left-winger and prominent supporter of Mr Corbyn's campaign for the Labour leadership.
Mr McMahon, leader of Oldham Council, said he was "delighted to be selected", while Mr Corbyn offered his congratulations and said he looked forward to campaigning with him.
Mr Meacher held the seat in May with a majority of 14,738, taking a 54.8% share of the vote, with Ukip finishing second, polling 20.6%.