Ghana’s main opposition party has reacted with anger after one of its most influential leaders was sentenced to 20 years in jail, with hard labour, for illegal mining offences.

The New Patriotic Party (NPP) alleged that the landmark judgement against Bernard Antwi Boasiako, the party’s chairman for the Ashanti region, was politically motivated.

Popularly known as “Chairman Wontumi”, Boasiako is the first senior politician in Ghana to be convicted of illegal mining since the government began a crackdown on the practice in 2017.

As well as receiving a jail sentence, Boasiako, who had denied the charges, was ordered to pay more than $10,000 (£7,450) in fines.

He looked visibly shocked when the judge handed down the sentence in a court in the capital, Accra, on Monday.

The NPP politician was found guilty of “assigning mineral rights without approval” and “facilitating an unlicensed mining operation” through his company, Akonta Mining.

Ghana is Africa’s leading gold producer, but a large portion of the country’s waters and environment have been polluted by illegal mining, known as locally as “galamsey”.

Over the years, governments have attempted to tackle the problem, even deploying the military, to little effect.