For the first time, eggs and other products including oranges and bread rolls – will be sold by weight instead of by the number contained in a packet.
Last week, MEPs voted to bring an end to Britain's exemption from the metric policy despite objections from several UK members.
Eggs have traditionally been sold by the dozen or half-dozen because the old imperial measurements such as inches or pennies were calculated in groups of 12. But the new rules, to be introduced next year, mean that instead of packaging telling shoppers a box contains six eggs, it will show the weight in grams of the eggs inside.
Last night, Britain's Food Standards Agency criticised the European Parliament's move, claiming it put the UK on a potential collision course with Brussels.
An FSA spokeswoman said: "This proposal would disallow selling by numbers. Retailers would not be allowed to put "Six eggs" on the front of the box. If it was a bag of rolls, it would say "500g" instead of six rolls.
"It is important that information is provided in a way that is meaningful and beneficial to consumers. This issue is still being considered by EU member states and it will be some time before the regulation is finalised."
The move could cost retailers millions of pounds because of changes they will have to make to packaging and labelling, as well as the extra burden of weighing each box of food before it is put on sale. It is predicted that the extra costs will be passed on to shoppers through higher grocery bills.
Experts say it will be next year before the EU is able to bring in the controversial measure, which bureaucrats say is designed to help consumers make an informed choice when buying their food.
But the Federation of Bakers director Gordon Polson warned that it may be too late to change the rules, even though they will be debated further in the European Parliament.
Andrew Opie, food director of the British Retail Consortium, which represents 90 per cent of UK shops, said: "This is a bad proposal – we need to help consumers, not confuse them."