Thai police on Friday questioned the wife of a British journalist over his social media links to unflattering photos alleged to be of the kingdom's crown prince, in a country where insulting the royals carries heavy jail terms.

Detectives said the photos were fake and questioned Noppawan Bunluesilp, 39, the Thai wife of former Bangkok-based correspondent and strident Thai monarchy critic Andrew MacGregor Marshall, at a police station in the capital over her husband's posts linking to the pictures.

The Twitter and Facebook post linked to a web article in German tabloid Bild with photos apparently showing 63-year-old Crown Prince Maha Vajiralongkorn at an airport in Germany.

On Friday morning the link to the page was blocked in Thailand for carrying "inappropriate content".

Each charge of lese majeste -- insults, threats or defamation of Thailand's leading royals -- carries up to 15 years in jail. 

Local and foreign media based inside the country -- including AFP --- must routinely self-censor to avoid falling foul of the law.

"The pictures were doctored," said Thitirat Nongharnpitak, commander of Central Investigation Bureau (CIB).

The culprit is Andrew MacGregor Marshall who has violated lese majeste laws for several years," he said, adding "he has acted from overseas to attack" the royal family.

Police have confiscated a laptop, iPad and other documents, Thitirat said.

Marshall is an outspoken critic of the Thai monarchy and has written a book on the subject which is banned inside the kingdom.

He regularly posts commentary on social media that would be swift grounds for prosecution under the kingdom's harsh royal defamation law.

On Thursday he posted the German newspaper article carrying the alleged photos of the crown prince, who spends much of his time in Europe.

Marshall's wife was shown on television arriving at the police station carrying her young son on one arm.

"It's a huge shock," he told AFP from Hong Kong of his wife's questioning. 

"The key point is my wife is not involved at all in my journalism -- we've always been very aware that it may put her in danger because I am writing things which break the Thai lese majeste law," he said.

"We'd always been concerned that it might be dangerous for my wife to visit Thailand especially since the military coup but she hadn't seen her family for a couple of years."

The issue comes during a time of intense sensitivity surrounding the Thai royals, as the health of revered 88-year-old King Bhumibol Adulyadej wanes.

The arch-royalist Thai junta has previously been accused of intimidating the relatives of government critics.

Since seizing power two years ago the junta has used a range of tactics to reel in dissent, including laws that curb free speech, mandatory "attitude adjustment" sessions for its critics and intimidation tactics that have spawned self-censorship across much of the press.

Source: AFP