Anti-Thaksin Shinawatra groups, including the People's Alliance for Democracy, opposition parties, senators and academics said His Majesty had exercised his royal power in this way in October 1973. Then, he appointed Sanya Dharmasakti as prime minister after Field Marshal Thanom Kittikachorn resigned following demonstrations demanding an end to the military dictatorship.

The groups claimed the King could legitimately exercise his royal power again to replace Thaksin with a "better candidate".

However, on Tuesday the King said the current call for a royally sponsored prime minister failed to stand up to democratic principles, which do not give him the power to make such decisions.

Under the constitutional monarchy, the appointment of a prime minister requires another person to counter-sign His Majesty's endorsement.

His Majesty said in 1973 his action was still democratic because there was a House in place - the National Legislation Council (NLC) - to function under the constitution. NLC vice president Thawee Rangkham countersigned Sanya's appointment, which made it legitimate under constitutional rules.

Under the current charter, the King would be required to appoint the prime minister from House members, and the House speaker would have to countersign the royal command.

Anti-Thaksin groups have called on the King to appoint a prominent figure who is not an MP to replace Thaksin. However, there is no one who could be officially authorised to countersign the royal appointment and the charter

does not include another mechanism by which the King could appoint a premier under the circumstances.