Chancellor Rishi Sunak has mistakenly joined a Tory rebellion against the government over post-Brexit food import standards.
Mr Sunak voted digitally for a change to the Agriculture Bill that would have guaranteed a ban on chlorinated chicken and hormone-fed beef.
The amendment was defeated by 277 to 328, a majority of 51.
A source close to the chancellor blamed "teething problems" with a new online voting system.
"The chancellor did not intentionally vote against the government. He called the chief whip straight away to explain," added the source.
Several MPs made the same mistake in what was only the second time they have voted digitally.
The system - brought in to allow MPs to continue working during the coronavirus lockdown - does not allow MPs to change their vote once it has been cast.
Deputy Speaker Dame Eleanor Laing said she had been told some MPs had mistakenly voted the wrong way and "that their use of technology was not quite as good as they felt that it ought to be".
But she told MPs she was "satisfied" the mistakes had not affected the outcome of the vote.
Ministers say the issue of protecting food standards in post-Brexit trade will be dealt with in the upcoming Trade Bill.
But opponents of practices such chlorine-washing chicken say that could lead to farm standards being bargained away in negotiations.
Instead, they wanted ministers to guarantee food standards in the Agriculture Bill.
Leading rebel, Tory MP Simon Hoare, warned MPs that without changes to the bill "food imports to this country would be cheap for no other reason bar the fact that they were raised to lower standards".
Fellow rebel Neil Parish, chairman of the Environment, Food and Rural Affairs Committee, told MPs it was time to support such measures.
He said: "I'd say to the Americans, why don't you upgrade your production? Why don't you reduce the density of population of your chicken?
"Why don't you reduce the amount of antibiotics you're using and then you can actually produce better chicken not only for America, it can also come into this country?
"Let's not be frightened of putting clauses into this bill that protect us to have the great environment and welfare that the whole bill wants to have and farmers want to have."
But Environment Minister Victoria Prentis warned of "unintended consequences" of amending the bill and insisted all EU import standards will be converted into domestic law by the end of the December 2020 transition period.
She told MPs all existing import requirements would continue to apply, including "a ban on using artificial growth hormones in beef".
She added: "Nothing apart from potable water may be used to clean chicken carcasses and any changes to these standards would have to come before this Parliament.
"We will be doing our own inspections to ensure that these import conditions are met."
Shadow environment secretary Luke Pollard said not including food standards in the bill could lead to a "race to the bottom".
During the third reading vote, Labour spokesman Mr Pollard could be heard asking in the Commons chamber: "How many members of the Cabinet voted the wrong way?"
Government deputy chief whip Stuart Andrew was heard replying: "Just the one. He's a very busy man."