He said: “I have to say these comments reveal a fairly unpleasant, careless elitism that somehow suggests that we should give up on a whole swathe of our fellow citizens.”
Mr Johnson said some people would always find it easier to get ahead than others arguing that IQ tests are relevant to “a conversation about equality.” He said, in the speech to the Centre for Policy Studies “many as 16 per cent of our species have an IQ below 85, while about 2 per cent have an IQ above 130.”
However Mr Clegg said this amounted to Mr Johnson treating people like a “breed of dogs.”
He added: “I think the danger is if you start taking such a deterministic view of people and start saying they’ve got a number attached to them, in this case an IQ number, somehow they’re not really going to rise to the top of the cornflake packet, that is complete anathema to everything I’ve always stood for in politics.
"There are people, certainly young people, who develop at different paces, who might discover talents they didn't know about before and our job, surely, in politics is not to simply say, look, we're going to hive off one bunch of people and put them in one kind of category, and kind of basically say they're parked and there's not much we can do about them”.
In his speech Mr Johnson also repeated warnings against persecuting the rich, saying that wealth and success should be celebrated.
None the less, he suggested that the gap between rich and poor had grown too wide and more must be done to ensure that talented people from less wealthy backgrounds can “rise to the top”.
Mr Johnson said: “I worry that there are too many cornflakes who aren’t being given a good enough chance to rustle and hustle their way to the top.”