LONDON -- A novelist, a duchess and a tabloid newspaper have ignited an explosive debate in Britain: Is it all right to criticize a pregnant Kate?

The Daily Mail on Tuesday ran a front-page broadside against two-time Booker Prize-winning author Hilary Mantel for what it called her "venomous attack" on the former Kate Middleton, now the Duchess of Cambridge.

Within hours, the Internet was ablaze. Prime Minister David Cameron joined in the criticism of Mantel while others rushed to her defence.

In a speech earlier this month, the writer had characterized the 31-year-old wife of Prince William as "a jointed doll on which certain rags were hung ... a shop-window mannequin, with no personality of her own."

Mantel said that Kate, as a royal consort, "appeared to have been designed by committee and built by craftsmen, with a perfect plastic smile and the spindles of her limbs hand-turned and gloss-varnished."

Mantel's speech, reprinted this week in the London Review of Books, was about the British public's complex relationship with royalty over the centuries -- a relationship both symbiotic and voyeuristic.

The speech looked at the way the public and the press both glorify and destroy royals, from Anne Boleyn to Princess Diana, casting them in roles and stories in which "adulation can swing to persecution, within hours."

But for the Daily Mail, this became "an astonishing and venomous attack on the Duchess of Cambridge."

The newspaper's front page juxtaposed pictures of the author and the duchess alongside the front-page headline: "A plastic princess designed to breed."

It quoted Mantel's speech at length, although it did not note that the 60-year-old author was describing what she saw as a view of Kate constructed by the press and public opinion.

Online reaction was divided, with some defending Mantel's words as provocative and thoughtful and others calling them hurtful.

Cameron -- on a trip to India -- said Mantel's comments were "completely misguided and completely wrong."

Claudia Joseph, author of "Kate: The Making of a Princess," said it was unfair to describe Kate as lacking in personality. Joseph said the duchess was instead someone who "has learned to keep her feelings hidden and private."

"The reason William chose Kate is because she is discreet and doesn't show her feelings in public," Joseph said. "That doesn't mean she has no feelings."

Others argued that Mantel's real target was not Kate but the press. On the Daily Telegraph website, journalist Catherine Scott said Mantel's speech was "an attack on how some parts of the media canonize royal women ... while also rendering them voiceless and purposeless."

The royal couple's office declined to comment.

Meanwhile, large numbers of journalists and photographers were on hand Tuesday to watch the duchess as she visited a centre for recovering addicts. It was one of her first public appearances since announcing in December that she was pregnant. News reports commented on the duchess's baby bump, gestures, demeanour and Max Mara dress.

Mantel won the prestigious Booker Prize in 2009 for "Wolf Hall" and in 2012 for "Bring Up the Bodies," novels set at the court of King Henry VIII and centred on the king's search for a queen who will give him a male heir.

Her speech touched on royal figures from Henry's wife Anne Boleyn to Kate.

Mantel said Diana "passed through trials, through ordeals at the world's hands." She said Diana's younger son, the 28-year-old Prince Harry "doesn't know which he is, a person or a prince" -- a confusion Harry himself recently remarked on.

And Kate, whose first child is due in July, finds herself cast by the press as someone whose "only point and purpose (is) to give birth," the author said.

Of the U.K.'s royal family, Mantel said "however airy the enclosure they inhabit, it's still a cage."

Mantel ended her speech -- ironically, given the media furor now -- with a plea for us all "to back off and not be brutes."