Douglas Carswell: UKIP needs a 'fresh face' as leader
Douglas Carswell has told the BBC that the UK Independence Party needs a "fresh face" as leader, with "an optimistic message" for the future.
UKIP's only MP said it "needs to change gear and to change its management if it's to go the next level".
The Clacton MP did not mention leader Nigel Farage, but told BBC Essex "no party is defined by any one person". He has ruled out doing the job himself.
Mr Farage told the BBC Mr Carswell should "put up or shut up".
He said it "hasn't hit me cold - he has been saying this privately for some months" but he insisted the party was "very united"
"We have one person who disagrees with my leadership - Douglas Carswell is out on a limb."
He has said he will not be sacking Mr Carswell from the party, however, and called on Mr Carswell to "stop sowing division".
Mr Carswell - who defected from the Conservatives to UKIP in August 2014 - made his comments to Nihal Arthanayake for a BBC Essex documentary following the MP around his constituency and Parliament.
Mr Carswell said UKIP "needs to change gear and to change its management if it's to go the next level".
He said the result of the Oldham West and Royton by-election, in which the party came a distant second to Labour after being tipped to run them close, "to me said, very clearly, that I think we need a fresh face".
In a reference to Mr Farage's claim that the Oldham by-election postal vote was rigged, he added: "I don't want to wake up the morning after the European referendum and hear it was the postal votes."
Mr Carswell, the party's first elected MP, said "a lot of people recognise there are a lot of talented people in the party", adding that "no party is defined by any one person".
By BBC Political Correspondent Iain Watson
You'd think it would be hard to have splits when a party has only one member of Parliament.
Douglas Carswell's defection from the Conservatives in 2014 undoubtedly gave UKIP a pre-election boost.
But since then, Nigel Farage must be wondering if he's more trouble than it's worth.
He has muttered about Mr Carswell's alleged "residual loyalty" to his Conservative friends and he was irritated by his sole MP's decision to campaign against European Union membership with the broad-based Vote Leave campaign rather than Leave EU, which is part-funded by UKIP donor Aron Banks.
Mr Banks had been overheard, during an exchange of views at this year's UKIP conference, suggesting Mr Carswell was "borderline autistic".
For his part, Douglas Carswell has called for Mr Farage to take a break from his leadership duties - but has now gone one step further and suggested a permanent change of management.
I understand that not only does he not want to be party leader himself, he isn't trying to launch a coup on anyone else's behalf.
So the MP leaves his current leader wounded going in to an EU referendum, but in place.
Perhaps it's little wonder Nigel Farage would rather he "put up or shut up".
In May, when Mr Farage returned as leader after his brief resignation, Mr Carswell said he should "take a break" and another senior figure, Patrick O'Flynn MEP, described the UKIP leader as "snarling, thin-skinned and aggressive".
But Mr O'Flynn rallied behind the party leader, following Mr Carswell's comments, saying it would not be "sensible" for UKIP to launch a leadership contest with the EU referendum coming up.
He said: "Nobody has done more than Nigel Farage to bring about this referendum and in my view he has a major role to play in the campaign and has earned the right to lead UKIP into it."
UKIP deputy leader Paul Nuttall said Mr Carswell would be "humiliated" in any leadership contest.
Douglas Carswell ruled himself out of the leadership saying he did not have the "patience".
He also ruled out leaving the party and becoming an independent MP saying: "I am 100% UKIP and I'm very committed to UKIP, I'm not going anywhere."
Douglas Carswell told BBC Essex the party had been "phenomenally successful" to be polling about "13%" during Mr Farage's tenure at the top of the party.
But he called for UKIP to become a party that is not seen as "unpleasant" and "socially illiberal".
Instead, Mr Carswell said that the party would "break out from the 13%" if it was an "optimistic, sunshine, smiley, socially liberal, unapologetically free market party".
"We will break out of being the 'also rans' in Oldham to the winner," he added.
He told the BBC that as a party of anti-politics it was natural for UKIP to appeal to people who feel disaffected.
But he said appealing by "playing back the tape of disaffection to them and play on that anger… you can do that and you can come second and you can carry on coming second and you can be an 'also ran'", he added.
Mr Carswell - UKIP's only winning candidate in the 2015 general election, despite the party getting nearly four million votes across the UK - urged UKIP to accept the reasons for its election losses rather than "blame voters".
"Let's not do what we did the day after the Oldham by-election and blame the voter, let's not pretend it's all due to postal ballots. You know they had postal ballots here in Clacton too and I don't remember anyone blaming postal ballots then.
"If you are in the business of doing democracy for a living you need to accept the democratic verdict, and the punter didn't take what we had to offer."