Millions of eggs have been recalled in Belgium, the Netherlands and Germany after they were found to contain the toxic insecticide which can cause damage to the liver, thyroid glands and kidneys if ingested in large amounts.
European Commission spokeswoman Anna-Kaisa Itkonen said she could not comment on the Belgian delay "because it's an ongoing criminal investigation".
Belgium's agriculture minister meanwhile said he had ordered the country's food safety agency to report by Tuesday on why it failed to notify neighbouring countries until July 20 despite knowing about fipronil contamination since June.
Around 85% of eggs consumed in Britain are home-produced.
On Monday a Dutch farming group said millions of hens may need to be culled in the Netherlands after traces of fipronil were found in eggs there.
It did not give a number but said it represented 0.0001 percent of eggs annually imported into Britain.
In the dark and silent shed of a small Dutch poultry farm, 1.8 million eggs closely packed together wait to be destroyed.
The watchdog initially stated on Friday (4 August) there was "no evidence that UK-produced eggs are affected or that contaminated products have entered the United Kingdom market".
Belgian and Dutch authorities are now investigating how the insecticide came into illegal contact with egg-laying chickens.
About 180 poultry farms in the Netherlands have also been temporarily shut in recent days while investigations are held.
The Dutch food authority (NVWA) also shuttered 138 poultry farms - about a fifth of those in the country - and warned that eggs from another 59 farms contained high enough levels of fipronil that it warned they should not be eaten by children.
But it is banned from being used to treat animals destined for human consumption, such as chickens.
The French minister for agriculture and food (ministère de l'agriculture et de l'alimentation) confirmed that the problem has "to date" not yet spread to France, although one breeder in the Pas-de-Calais is under investigation after informing the authorities that the offending substance - the insecticide fipronil - may "potentially have been used" in its operation.