The Food Standards Agency has rejected claims that it was "asleep on the job" by not detecting the presence of horse DNA in processed meat products sooner.
But its chief executive, addressing the agency's board meeting, said the body had to ask whether it should have been "more alert" to the risks of possible contamination.
Catherine Brown told the FSA board: "We have been irritated by suggestions that we were in some way asleep on the job, suggestions that come from those who speak with the benefit of perfect hindsight.
"I have yet to see any evidence of someone highlighting, whether in public or private, that this was likely to happen. And this criticism ignores the fact that if we missed something, so did our counterparts in every European member state and every food business in the UK and in Europe."
Ms Brown said the FSA would have to improve how it investigated possible risks in the food chain. She praised the UK reaction to the horse meat scandal, saying it "dwarfs the response in other European countries", but said the scope of the FSA's power needs to be considered and will be discussed at the next board meeting.
Consumer confidence has suffered since the news of the contamination broke, with sales figures reflecting that, the board heard. "There is a real challenge for us and for the food industry to address consumer confidence in the coming months and make sure consumers have well-founded confidence in the food they eat," added Ms Brown.
FSA chairman Jeff Rooker said consumers had been left feeling "cheated" by those who mislabelled meat products containing horse DNA. "They have fiddled the books and cheated the public, and the public have every right to be damned annoyed about it," he added.
Many of the UK's biggest food firms and supermarkets have recalled beef products after tests found they contained horse DNA. Frozen food company Birds Eye has named an Irish meat processor as the source of horse meat contamination in three of its products. Birds Eye said QK Meats supplied meat with horse in it to Frigilunch NV, who used it in products supplied to the company.
Later, ABP chief executive Paul Finnerty, whose company supplied Tesco with beefburgers that turned out to be 29% horse, told the Environment, Food and Rural Affairs Select Committee it became clear overnight on January 14 to 15 that "we were out of specification" because product was coming in from a combination of suppliers that were not approved.
Asked how long he thought this had been going on for, he answered: "I think it had been going on for a number of months."