The DIY SOS host asked a magistrate if he was allowed to drive home - despite being banned from the road moments earlier.
The 56-year-old was fined almost £1,500 and given six points on his licence, which resulted in a driving ban as he already had six points on it.
Presiding justice Andrew Hill told Knowles: "From this moment in time, you are not able to drive any motor vehicle in any public place."
Knowles asked: "I can drive home, right?"
Mr Hill replied: "No."
Knowles then told him: "I'm joking."
The presenter and former I'm A Celebrity... Get Me Out of Here! contestant admitted driving at 85mph in his Range Rover while using his mobile phone, on 28 January.
He told Cheltenham magistrates he had a hands-free kit in his car but was holding his phone due to a "dodgy power lead".
He was fined £666 for speeding and £666 for using his phone, with a victim surcharge of £66 and prosecution costs of £85.
Mr Hill said Knowles had 28 days to pay the total amount of £1,483.
The court heard he had pleaded guilty to both offences in May, under the single justice procedure.
Knowles, representing himself, said he had chosen to "dismiss" legal advice to attempt to "get by on a technicality".
"I was travelling faster than I should have done," he told magistrates.
"I do 25,000 miles a year and at various other times, I have looked at my phone.
"I had fallen into the habit of looking at texts. I now put my phone in the boot of my car."
Speaking outside court, Knowles described the incident as a "wake-up call".
"The six-month ban was appropriate because to give anything else would be giving me special privilege," he added.
Knowles said he hoped his case would make other people alter their behaviour too.
© Sky News 2019