Watchara Petchthong filed a lawsuit against Nattawut Saikua, Veerakarn Musikapong and Jatuporn Prompan, leaders of the United Front for Democracy against Dictatorship (UDD), accusing them of defaming him on their TV programme in 2012.

The lawsuit centred on changes to a book cover concerning the late prime minister Samak Sundaravej, who led the red-shirt-backed People Power Party, a successor to the defunct Thai Rak Thai Party. Red-shirt figures claimed the changes were made after Samak died.

The book cover referred to Samak criticising a prominent figure. Red-shirt demonstrators later went to Watchara’s party office to demand that he issue an apology to the late prime minister.

The court found that their accusation against the MP was groundless and the accusation was also provocative.

On those grounds the Appeals Court upheld the Justice Court’s original ruling and the sentences.

Jatuporn was jailed on Tuesday after a court revoked his bail in another defamation case, but he was brought to the Appeals Court hear this ruling.