Forty-eight developing countries – including Bangladesh, Sierra Leone, Haiti and Ethiopia – will continue to benefit from the arrangements on all goods bought by the UK, excluding weapons.
Some £20bn a year of goods are shipped to the UK from these countries, accounting for around half of UK clothing, and a quarter of UK coffee.
The Government said that once it has left the EU in 2019 it will explore options to expand trade relations further.
International Trade Secretary Liam Fox said: “Our departure from the EU is an opportunity to step up to our commitments to the rest of the world, not step away from them.
“Free and fair trade has been the greatest liberator of the world’s poor, and today’s announcement shows our commitment to helping developing countries grow their economies and reduce poverty through trade.
“Behind the ‘duty-free exports’ are countless stories of people in developing countries working hard to provide for themselves and their families by exporting everyday goods such as cocoa, bananas and roses, resulting in lower prices and greater choice for consumers.”
The Fairtrade Foundation’s Tim Aldred welcomed the Government’s pledge to increase trade with developing countries in a number of areas.
He said: “We are very pleased to hear today’s commitments to guarantee and strengthen the position of the least developed countries who provide such a high quantity of the goods sold in our supermarkets and high streets.
“The position of poor countries just outside the ‘least developed country’ category, such as Kenya, will need to be clarified.
“Government will also need to take care that large deals with emerging economies do not push out the sales from the poorest countries.”