Sadiq Khan has taken a major swipe at Rachel Reeves, accusing the Chancellor of talking down the country.
The mayor of London argued Ms Reeves has to change her approach if Labour wants to recover from their disastrous local elections last Thursday.
The Labour Party lost over 1,200 seats, more than half of those it was defending, along with 37 councils.
The Greens won their first-ever London council seats, taking Hackney, Lewisham, and Waltham Forest from Labour, and the directly elected mayoral seats in Hackney and Lewisham.
Reform UK also gained its first London council majority in Havering.
The Conservatives regained control of Westminster from Labour, and the Liberal Democrats won all 54 seats in Richmond upon Thames.
Speaking on the reasons behind the poor results for his party, Sir Sadiq said: "There was, without doubt, unhappiness with Keir Starmer, with the Chancellor Rachel Reeves, and with the Labour Government.
"We should be giving hope."
Sadiq Khan has taken a major swipe at Rachel Reeves, accusing the Chancellor of talking down the country
|PA
He added: "I mean, this doom and gloom stuff, every time I hear the Chancellor speak, it’s doom and gloom for the last two years.
"People didn’t vote for a Labour Government for more doom and gloom.”
The Labour Chancellor has consistently blamed the previous Conservative Government for leaving a multi-billion pound "black hole" in the UK's public finances.
While initially citing a £22billion deficit upon taking office, the figure has since been disputed.
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The mayor of London argued that Ms Reeves has to change her approach if Labour want to recover from their disastrous local elections last week
|PA
No10 has dismissed claims Rachel Reeves misled the public, but Conservative leader Kemi Badenoch accused Ms Reeves of "lying to the public" and called for her dismissal.
Mr Khan argued many investors, venture capitalists and chief executives across the world were put off from investing in Britain by Ms Reeves comments, despite Labour's landslide.
He told The New Statesman: "What’s bad is talking down our country, what’s bad is not being a great salesperson for this country.
"It’s really important to encourage people to come here, but to keep them when they come here.
The Labour Chancellor has consistently blamed the previous Conservative Government for leaving a multi-billion pound 'black hole' in the UK's public finances
|GETTY
Mr Khan added: "We are, inadvertently from the noise coming from the Treasury, encouraging people to leave this country to go elsewhere. It’s bonkers.
"We want wealth creators here, we want people who want to live here, we want to encourage the rights of people and businesses to come here, and when it’s all doom and gloom, why would you choose to come here?"
The Mayor of London also recently referred to Reeves as a "roadblock" to greater devolved powers in London.
He said: "You’ve got to support people whose living standards [need to be] increased, invest in public services, but you’ve also got to work with the private sector to help create wealth, jobs and prosperity.
"And I think my party in Government has lost the skill, doesn’t seem to have the art of being hopeful, optimistic, upbeat, and that’s what people want."