The outcome of the EU referendum, with the UK preparing to withdraw, has already created significant uncertainty for trading partners in developing countries.
Traidcraft says producers are already suffering – with the pound falling in value, their goods have become more expensive in the UK and aid, investment and remittances have lost value.
And when Britain does leave, producers face an increase in the cost of trading with the UK, reduced demand for their products and increased bureaucracy to meet the demands of multiple markets.
Britain imports £34bn of goods from developing countries – and 47% of these could face extra tariffs after Brexit, with and extra £1bn imposed in import taxes.
There are also concerns about the effects of new trade deals which the UK is looking to sign.
Stirling Smith from the Co-operative College said: “The problem is that if the UK is going to go for bilateral trade deals, they are very unlikely to put into this the question of workers’ rights to international labour standards.
“They are not going say, ‘We would like to see you improve labour standards.’ The EU is not great at doing this but at least it’s on the agenda and they have withdrawn various sustainable development and good governance (GSP) arrangements from countries for standards of labour.
“So this will be lost from trade deals, which contradicts the Modern Slavery Act – one of only May’s only achievements as a home secretary.”
Traidcraft is lobbying MPs to write to the international trade secretary, to call for a fair deal for poor farmers and workers in developing countries as well as for consumers in the UK.
It also wants a “gold standard for development-focused trade policy”, with “non-reciprocal preferential market access for developing countries”.
Future trade negotiations should support sustainable development, it adds.