A drug widely used to cure malaria has failed for the first time in patients being treated in Britain, raising questions over whether the parasite is becoming resistant to drugs, researchers said today.

Four patients who contracted malaria in Angola, Liberia and Uganda had to seek alternative medicines after the drug they were given to combat the mosquito-borne disease failed, the London School of Hygiene and Tropical Medicine (LSHTM) said in a study.

"This is concerning and may indicate that there's a bigger story beginning to emerge in Africa," Colin Sutherland, a medical researcher from the LSHTM, told the Thomson Reuters Foundation.

"It may be an early warning that we need to change a few things," he said, calling for more research into the efficacy of the Artemether-lumefantrine drug.

Sutherland said he had heard anecdotes from colleagues in Africa who had also seen resistance by parasites to the drug, saying the cases seem to be developing in different parts of the continent slowly.

Sub-Saharan Africa carries a disproportionately high share of the global malaria burden and in 2015 was home to 90 per cent of malaria cases and 92 per cent of malaria deaths.

While deaths from the disease have fallen dramatically in the past 15 years - since 2000 malaria deaths in Africa have dropped by 62 per cent - to 429,000 in 2015, there are big gaps in progress, with the poorest countries faring the worst.