Natalie Bennett overshadowed her own party's general election campaign launch after an "awkward" and "awful" radio interview on housing policy.
The Green leader blustered when she came under tough questioning from LBC Radio's Nick Ferrari.
The host quizzed Bennett over her party's manifesto pledge to build 500,000 new social-rent homes by 2020.
The Greens claim that there is a lack of affordable homes and "urgent action" is required to address the housing shortage.
But Bennett crumbled under Ferrari's scrutiny when he asked the leader about the Greens' costings.
"We want to fund that by removing the tax relief on mortgage interests on private land lords," Bennett said. "Private landlords at the moment are running away with the situation of hugely rising rents, they are collecting large amounts of housing benefit."
The LBC presenter then pressed the Green leader on how much the mortgage relief for private landlords would raise.
"That's part of the whole costing of this," Bennett replied.
Ferrari repeated his question but the Australian-born politician was not able to give a definitive answer.
Instead, Bennett claimed that the total cost of the housing programme would amount to £2.7bn ($4.1bn, €3.6bn).
"Right, what we are looking at, in terms of the figures here...what we need to do actually is... we're looking at a total spend of £2.7bn," she said.
The radio host did not let up and queried the £2.7bn, asking if the houses would be made of "plywood."
"Basically, what we are talking about is 500,000 new homes and, basically, each £1 spent on this brings back £2.40," Bennett said.
The Green leader went on to claim that the homes would cost £60,000 each, but Ferrari questioned if that figure included the cost of the land.
Bennett: "Well, what we're talking about is the possibility of homes..."
Ferrari: "That's not much more than a large conservatory, £60,000. How are you going to pay for the land?"
Bennett: "...Right, well, what we are looking at doing is, basically...[coughs]...as you can probably hear, I've got a huge cold."
Social media users took to Twitter to blast Bennett for the "awkward" and "awful" interview.
"My God this Nick Ferrari interview with Natalie Bennett is awful," said Ian Dunt, editor of Politics.co.uk.
Mark Ferguson, editor of LaburList, described the episode as "like watching someone punch their own face".
The interview will be a distraction from the Greens' general election campaign launch today (24 February), where the party is expected to announce that it is committed to a "citizen's income" of £72 for all adults.
The announcement comes with 72 days to go before the general election in May, with the Greens on 7%, the Liberal Democrats on 8%, Ukip on 13%, and the Tories and Labour neck-and-neck on 33%.