The Supreme Administrative Court has ruled against Pol Gen Sereepisuth Temeeyaves, leader and list-MP of the Seri Ruam Thai party, ordering him to dismantle a structure at his house which it says encroaches on the Kwai Noi River in Kanchanaburi.
The judgement, handed down on Friday, involves a decade-long dispute between Pol Gen Sereepisuth and six agencies including the Marine Department over the river encroachment in Thong Pha Phum district.
Pol Gen Sereepisuth, a former national police chief, had been served notice by the department to dismantle the structure which he built at his river house without permission.
He reclaimed a stretch of land covering 1,500 metres by dumping debris onto the riverbed, the court said, dismissing claims he reclaimed it naturally.
The former police chief challenged the order with the Administrative Court which ruled in the department's favour in 2014.
He then appealed to the Supreme Administrative Court, which also dismissed his case and ordered him to remove the structure within 30 days.
The Supreme Administrative Court dismissed Pol Gen Sereepisuth's claim that he reclaimed the stretch of land by natural means.
He claimed he had sought and secured the department's permission to dump rocks to protect the eroding bank.
According to the court, Pol Gen Sereepisuth in fact hired people to dump debris into the river to create the stretch of land where he built a small garden.
The activity was in violation of the permission originally granted by the department, according to the court.
The court said the notice for him to dismantle the structure was legitimate and dismissed his petition. It is unclear what deadline he faces to get it done.