The BBC presenter pilloried the mayor after Transport for London introduced the toxin charge which will see drivers of the oldest and most polluting diesel and petrol cars forced to pay a daily fee to be able to use their vehicles in London.
Speaking on the BBC Radio 4 Programme, Mr Webb said: "The bad news, surely, is that it won't actually change the quality of the air in London very much.
"On this particular change today, it's not going to change things much. it's just going to make it much more expensive for some people, some private motorists, to bring their vehicle into London and apart from that it won't have a big impact."
NEWGATE COMMUNICATIONS/FOX NEWSMr Webb told Mr Khan the t-charge will have no immediate impact on London's air quality
Mr Khan introduced the T-charge in an attempt to reduce the dangerous levels of air pollution in the Capital.
Ahead of the T-Charge launch, the mayor revealed that every Londoner is