One of Labour's would-be MPs has faced criticism after suggesting leader Ed Miliband will "never form a credible government" unless he does more to win over "the aspirational southern voter".

Tristan Osborne, the Chatham and Aylesford prospective parliamentary candidate, hit out at his own party and what he described as "a dodgy campaign", according to a national newspaper report.

He alleged the party machine "is not functioning in any capacity" and questioned the party's key message over the "cost of living crisis".

Chatham and Aylesford will be a key electoral battleground in 2015 and Labour is targeting the constituency that it lost to the Conservatives in 2010. Tracey Crouch MP has a 6,069 majority.

Mr Osborne was unaware his comments were being recorded at a party fundraising event in London.

"We need to be appealing to the aspirational southern voter... the current strategy doesn't seem to indicate that we are winning over that type of support, and that is the issue... the machine is not functioning in any capacity..." - Tristan Osborne

He was also reported to have said the party could do "sod all" to combat a Tory campaign focusing on rising economic growth.

In the recorded conversation, he said the campaign was "very tough".

He said: "We need to be appealing to the aspirational southern voter... the current strategy doesn't seem to indicate that we are winning over that type of support, and that is the issue... the machine is not functioning in any capacity."

Mr Osborne added: "We need to target aspirational southern voters. That's where you win elections... If you don't win areas like Norwich, Croydon Central, Chatham, Harlow, you're never ever going to form a credible government."

He suggested Labour's decision to campaign on the cost of living would not be enough to win key target seats in the face of an improving economy.

"I don't know how Labour counters that, I just don't know. How do you counter a positive economic message which is totally out of your control? The economy is picking up — that's nothing to do with the Tories... but that reinforces the narrative that they are doing well and there's absolutely sod all anyone can do about that.

"Labour can chisel away at the cost of living and that will work with some groups, but not groups you need to win — these are people who voted Labour before."

The candidate said he was encouraged that Labour is "still equal or slightly ahead" in national polls.

"We do need to win in the south," he said. "I want us to be communicating a very coherent message around that... absolutely, we need to have a strategy to do that. I'm a southern candidate. I would say that. We've got a year to go before the election and I want to make sure that message is absolutely communicated."

Mr Osborne could not be reached by the KM Group to comment. However, he did not deny making the comments when contacted by The Sunday Times.

But Dover Conservative Charlie Elphicke MP weighed in to attack the remarks said: "Even Labour's top candidates despair at Ed Miliband's lack of any coherent plan for the country."