Former British Army officer and mercenary Simon Mann, who was part of a coup attempt in Equatorial Guinea in 2004, has died of a heart attack while exercising, friends confirmed.

The 72-year-old made millions of pounds from protecting businesses in conflict zones before he took part in the failed attempt to overthrow the west African nation’s ruler.

Mann was sentenced to 34 years in prison on arms charges and later said he had been the “manager, not the architect” of the scheme.

In 2009, the ex-SAS commando was pardoned, released and given 48 hours to leave the country.

The plot had been an attempt to overthrow President Teodoro Obiang Nguema – at the time Mann and co-conspirators said the aim was to install exiled opposition leader Severo Moto.

It was uncovered after police in Zimbabwe’s capital Harare impounded a plane which had flown in from South Africa.

Mann and more than 60 others were arrested, amid claims they were mercenaries.

They said they were providing security for a mine in the Democratic Republic of Congo.

Mann attended private boys’ school Eton before studying at Sandhurst Royal Military Academy and then joining the Scots Guards.

He became a member of the SAS – the army’s special forces unit – and rose through the ranks to become a commander.

In 2011, he said the attempted coup in Equatorial Guinea – which saw him arrested with fellow mercenaries after trying to load weapons onto a plane in Zimbabwe – was foiled by the CIA.

After serving three years of his 34-year sentence in Zimbabwe, he was moved to Black Beach Prison in Equatorial Guinea.

Speaking in 2011 about that move, he said “friends, family, and enemies” had told him “if that happens, you have had it, you’re a dead man”.

After being pardoned and released, he expressed regret for what he had done, saying that “however good the money is”, the moral case “has to stack up”.