London mayor frontrunner Sadiq Khan has refused to address claims made by Lord Sugar that he has "single-handedly wrecked the Labour Party".
The Apprentice host and former Labour peer launched a blistering attack on Mr Khan, branding him and Jeremy Corbyn the "Laurel and Hardy" of politics.
Lord Sugar, who quit Labour to become a non-affiliated peer in protest at what he called its anti-business stance under Ed Miliband, warned Mr Khan would be a disaster for London if he wins the May 5 showdown with Tory Zac Goldsmith.
Labour now welcomes anti-Semites and terrorist sympathisers to its ranks, the TV star warned.
"I would say Khan has single-handedly wrecked the Labour Party, and now he's turning his finely-honed judgment on the great city of London," the peer wrote in The Sunday Times.
Asked about how the article made him feel and what he would say to Lord Sugar, Mr Khan told the Press Association during a campaign visit to Brixton: "I want to be the most pro-business mayor London's ever had. I've got support from across London - chief executives, start-ups, entrepreneurs, as well as bus drivers, cleaners, teachers."
When it was put to him that Lord Sugar is considered to be a very powerful man, and asked if he has worries that his comments will influence people, Mr Khan said: "I've been working my socks off for the last few months speaking to business leaders, those who've started a business, those who run a business, and what's quite clear is they want a mayor of London who's going to be pro-business, who understands the challenges they face, the aspirations that they have."
He said that is one of the reasons he will set up a skills-for-Londoners programme.
"That's one of the reasons why I think it's really important that we stay in the European Union," he added.
Pushed on whether he was going to comment on what Lord Sugar wrote, Mr Khan said: "I'm going to have a positive campaign for the next 10 days like I've had for the last three months, and hopefully Londoners will choose the most pro-business mayor ever."
In the article, Lord Sugar wrote: "Khan ran Ed Miliband's leadership campaign. He was in the room when Miliband turned on people like me, attacking the country's largest employers as 'predators', as well as Corbyn, who famously called Britain's businesses the real enemy.
"Khan was one of the most senior Labour politicians to nominate Corbyn for leader. Without Khan's endorsement, Corbyn would never have made it onto the ballot.
"Under Corbyn, the lunatics have truly taken over the asylum. His ambition is to drag Britain back to the 1970s - union blackmail and three-day weeks, when our best and brightest were leaving the country in droves. Militants, Trots, anti-Semites and terrorist sympathisers all seem to have been welcomed into Labour with open arms," the peer said.
Lord Sugar said Mr Khan will not be independent of the Labour leader, as he accused Mr Corbyn of being on friendly terms with terror groups like Hamas.
Mr Khan has repeatedly condemned Tory claims he showed poor judgment in sharing platforms with extremists.