Green Party leader Natalie Bennett has apologised to party members for what she said was a "very bad" radio interview about its housing policy.
Ms Bennett said she had suffered a "mind blank" during the "excruciating" exchange, where she tried to explain how the party would fund a pledge of 500,000 new social rental homes.
She was speaking as the Greens launched their election campaign.
Other policies include a "citizen's income" of £72 a week for all adults.
During an interview on LBC, Ms Bennett seemed to struggle to explain the funding model for the new homes, saying she had a "huge cold".
Later, speaking on the BBC's Daily Politics, she said a fully costed manifesto would be published in March.
"I had a very bad interview on housing this morning," she said.
"I am very happy to confess that and I am very sorry to the Green Party members who I did not do a very good job representing our policies on.
"That happens, I am human."
The policy would cost £27bn, she said (although she had earlier mistakenly said £2.7bn in the LBC interview) which would be partly funded by removing tax relief on mortgage interest for private landlords.
The Green Party of England and Wales has seen its membership surge to 54,000, as Ms Bennett has switched focus from its traditional environmental policies to talk about inequality and social justice.
It has been recording similar levels of support to the Lib Dems in opinion polls and is fielding its largest ever slate of candidates, aiming to stand in 90% of parliamentary seats on 7 May.
Replacing the existing benefits system with a "citizen's income" paid to everybody in the UK is a longstanding Green policy.
There was speculation that the policy was going to be dropped but in an interview with BBC Radio 4's Today programme, Ms Bennett confirmed it would be in the party's election manifesto.
She said it was not something the party would expect to introduce overnight "or even within the term of the next Parliament", adding: "It's something we want to consult on, offer over time."
She added that she wanted to "move away from a system where so many people are living in fear of not being able to put food on the table, not being able to keep a roof over their head".
Pressed on how the party would pay for the policy, she declined to say how much it would cost but said there would be a "consultative costing" in March.
Ms Bennett is also campaigning for a 1% "wealth tax" on the property, pension pots and other assets such as "holdings in cash or Ferraris" of individuals worth more than £3m.
Launching her party election themes, Ms Bennett said "something profound" was happening in British politics.
The key themes the Greens say they will focus on during the general election campaign are:
- Rebuilding the economy so everyone gets a fair share
- Putting the public at the heart of the NHS
- Ensuring everyone has a secure, affordable place to live
- Taking action on climate change
- Investing in a public transport system
- Ensuring every young person who wants to can access quality education
The party currently has one MP at Westminster, Caroline Lucas in Brighton Pavilion.
It has held talks with the Scottish National Party and Plaid Cymru about forming a "progressive alliance" in the event of another hung parliament.
The Greens would make scrapping Britain's Trident nuclear weapons a key demand in any post-election negotiations with the Labour Party, in the event that Labour is the largest party.
But Labour said "the election choice is between Labour and the Tories".
Shadow Cabinet Office minister Jonathan Ashworth said: "A vote for the Green Party would increase the chances of the Tories remaining in Downing Street.
"When the Greens are put under any serious scrutiny their policies fall apart."