Thai protesters rallied in Bangkok yesterday evening to condemn a constitutional court decision to clear Prime Minister Prayut Chan-o-cha of wrongdoing for staying in army housing beyond his retirement as army chief.

Chanting "get out" and "evil prime minister", they alleged that Mr Prayut got preferential treatment. They also repeated their months-long demand that King Maha Vajiralongkorn stay above politics as would be expected in constitutional monarchies.

Earlier yesterday, the Constitutional Court said Mr Prayut was entitled to stay at the guest quarters in the First Infantry Regiment base in Bangkok, where he had been living before his retirement from the military.

"General Prayut Chan-o-cha can legitimately stay in the army guests facility... as a former army leader and as a person who serves the country," the court said.

If the court had ruled otherwise, he could have been thrown out of power.

In May 2014, the then army chief staged a coup that toppled the Pheu Thai Party-led government and installed himself as prime minister.

He retired from his military post in September that year, but continued to stay in the army quarters with his family.

After last year's election, he returned as premier heading the present coalition government.

Opposition lawmakers filed a complaint about his alleged abuse of power earlier this year.

Mr Prayut, 66, has said he is staying in the barracks for security reasons. He did not appear in court yesterday, choosing to make a field visit to Samut Songkhram province and then attend a meeting at the Government House.

Since February, youth-led protests have taken hold against the government, which demonstrators argue is a holdover from Mr Prayut's earlier regime that triumphed by dint of a specially engineered Constitution.

Apart from demanding that the Constitution be amended and Mr Prayut resign, protesters have also called for the monarchy to be reformed.

The last demand is the most controversial, given that King Vajiralongkorn controls two army units and personally owns assets estimated at over US$40 billion (S$53.6 billion) that used to be held in the name of the Crown Property Bureau.

While lawmakers voted last month to begin the process of amending the Charter, most have been reluctant to touch the powers of the monarchy.

The King, who usually spends much of the year in Germany, has been touring Thailand with Queen Suthida, and meeting and praising royalists close-up.

Meanwhile, the government has lifted a moratorium on lese majeste charges, which were brought by police against at least 12 protest leaders over the past week.

Under this law, anyone convicted of insulting or defaming the King, Queen or heir apparent can be jailed for up to 15 years.

The escalated police action did not deter protesters from rallying outside an army base housing a unit personally controlled by the King on Sunday.

At yesterday's rally, key protest leader Arnon Nampa, who has been charged under the lese majeste law, again took aim at the King.

"Many issues will arise if the monarchy is not politically neutral," he said on a stage designed to look like a court. He promised that the protests will continue into next year and the movement will grow.