A portrait of Thailand's King Maha Vajiralongkorn. Charges of insulting the monarchy in the country carry a jail sentence of up to 15 years

Police in Japan are investigating a bizarre attack on a dissident Thai scholar in what appears to be the latest example of violent persecution of exiled critics of the country’s controversial king, Maha Vajiralongkorn.

Pavin Chachavalpongpun, a Thai academic who lives in exile in Kyoto, says that he and his partner were attacked in their sleep by a man who broke into their apartment in the middle of the night and sprayed them with a chemical fluid. He believes that the attack last month was carried out at the behest of the Thai government and represents an attempt to intimidate him and discourage him from his outspoken criticisms.

“I truly believe that this has to be connected with Thai politics,” said Mr Pavin, who was