The world’s most coup-prone state risks renewed turmoil this week as a contentious referendum threatens to destabilise the Comoro Islands and draw France deeper into a migrant crisis that has bolstered its nationalist right.

The archipelago of Indian Ocean islands off south-east coast of Africa had seemed to have shaken off an era of chronic instability that saw 20 coups and coup attempts after independence from France in 1975.

But after 17 years of relative calm, a power-sharing agreement that restored peace between the state’s three bickering islands is facing deep strain after Azali Assoumani, the Comoran president, called a vote that could extend his hold on power by a decade.

For the opposition,…