Radio host and TV presenter Chris Tarrant was found to be over the drink-drive limit after he was reported to police by a fellow pub-goer.
The star had been served four brandy and ports at the Bladebone Inn in Bucklebury, Berkshire, before driving home, Reading Magistrates Court heard.
Tarrant, who admitted drink-driving, was banned from driving for a year.
After the hearing, he told reporters: "I made a mistake and I paid for it. I shouldn't have driven."
The Who Wants to be a Millionaire host was found to have 50 microgrammes of alcohol per 100 millilitres of breath. The legal limit is 35 microgrammes.
The 71-year-old said he "honestly didn't think" he had been over the legal limit when he got in his Mercedes to drive the short journey home, on 16 December.
'Stumbled near bar'
Prosecutor Hasrat Ali told the hearing that staff and drinkers at the pub were "concerned that he had decided to drive home".
"One member of the public had noticed that Mr Tarrant had stumbled near the bar area," she said.
As a result of a discussion in the pub, a member of the public phoned the police.
Thirteen minutes after the call was made, officers arrived at Tarrant's home in Osgoods Gully, Bucklebury.
Ms Ali said: "He claimed that he had just drank three glasses of wine just prior to police arriving."
But the court was told by Ms Ali that, after failing a breath test and being taken to the police station, Tarrant "gave a different version of events in the sense that it wasn't three glasses of wine that he had drank, that in fact he had a large glass of brandy and a glass of wine".
Tarrant's counsel Simon Ray said the drinks that were bought in the pub were not all consumed by his client.
He added that the TV presenter had a knee condition that explained the stumble.
District Judge Shomon Khan said despite the "relatively low reading" nothing he could say would "reduce the seriousness of the offence".
He also fined Tarrant £6,000.