Boris Johnson has denied he acted irresponsibly by allowing his two sons aged 11 and seven to sit together in the front seat of a sports car.
Mr Johnson leaves Old Trafford cricket ground in the Lamborghini
The Tory frontbencher was filmed by a Sun reader as he drove down the M6 in an open-topped Lamborghini.
The RAC accused Mr Johnson of being "grossly irresponsible" and said there should only be one person at a time in the front passenger seat of a car.
Mr Johnson told the London Evening Standard the boys had a seatbelt on.
"And I don't think they were in any danger," he added.
"If anyone says I was speeding, I want to see the evidence."
A spokesman for the Henley MP and Tory higher education spokesman told BBC News he would be making no further comment on the incident.
He said Mr Johnson had been road testing the car - a 195mph Lamborghini Gallardo Spyder - for men's magazine GQ.
"They normally give him a car every couple of weeks to road test," he added.
He said Mr Johnson had been driving north on family business.
The footage was posted on the Sun's website.
In the clip, taken with a camera phone, the unnamed Sun reader can be heard shouting "I love you Boris" as he drives alongside the car the MP is driving.
The newspaper quotes the man as saying: "I couldn't believe my eyes. If there had been a crash it would have been awful.
"But Boris didn't seem to give a damn."
An RAC spokesman said: "Our road safety consultant has said Mr Johnson was grossly irresponsible.
"You need to make sure your children are securely strapped and have booster seats if they need them.
"And, in any case, there should never be more than one person in the front passenger seat of a car."
Mr Johnson has two sons and two daughters.