Britain's senior diplomat in Bali has been suspended, the Foreign Office has confirmed, after a report of an affair with a drugs prisoner.

The Mail on Sunday newspaper reported that Alys Harahap was suspended over a relationship with Julian Ponder, a Briton serving time in the Indonesian island's notorious Kerobokan prison for possession of cocaine.

"We can confirm that a member of staff has been suspended pending the outcome of an investigation into these allegations, which we take extremely seriously," a spokesman for the Foreign Office in London said, declining to comment further.

The news comes amid growing concern over another British prisoner in Bali, Lindsay Sandiford, a 58-year-old grandmother sentenced to death in 2013 after being caught trying to smuggle cocaine on to the island.

Indonesia's new President Joko Widodo has been a vocal supporter of capital punishment for drug offenders.

The attorney-general's office said last week it was ready to execute seven foreign drug convicts on death row after their appeals for presidential clemency were rejected.