Natasha's Law has been enacted today requiring all pre-packed food to display full ingredient and allergen labelling from October 2021.
Legislation has been amended by the government and will apply to all food prepared and packed on the same premises from which it is sold.
The change follows the death of Natasha Ednan-Laperouse (pictured), who suffered an allergic reaction to a Pret A Manger baguette containing sesame. At an inquest into her death a coroner had described Pret's allergen labelling as "inadequate".
Natasha's parents Nadim and Tanya Ednan-Laperouse said: "This is a hugely significant day for allergen sufferers in this country. The introduction of Natasha's Law brings greater transparency about what people are buying and eating, lays down new standards for the food companies, and highlights the battle against the growing epidemic of allergies.
"Natasha was a spirited campaigner for justice and today she is smiling down on us knowing that this law well help ensure others do not suffer in the way our family does, and always will, following the loss of our beloved daughter and sister.
"We would like to thank ministers for their unflinching support in doing the right thing on behalf of all people with allergies."
Food minister Zac Goldsmith said: This is a significant moment for the millions of allergy sufferers in England and a fitting tribute to Nadim and Tanya Ednan-Laperouse's tireless campaigning.
The introduction of this law will make it easier for allergy sufferers to make clear, safe choices when buying food."
UKHospitality chief executive Kate Nicholls had previously warned that the legislation could be "unwieldy, difficult for some businesses to implement and potentially dangerous".
She had added: "We firmly believe the best way to raise awareness of allergens and keep customers safe is to promote an active dialogue between customers and businesses. That is why we recommended the promotion of voluntary labelling and encouraging customers to talk to the business and ask about ingredients and possible allergens. That way, we can build a relationship between consumers and team members that promotes mindfulness on both sides."
Heather Hancock, chair of the Food Standards Agency (FSA), has called on businesses large and small to work with it to meet the requirements of the new legislation.
The FSA is developing a working interpretation of the types of food to which this legislation applies, which will be published on 1 October.
The changes will apply in England, with similar arrangements expected to follow in the devolved nations.