Admittedly, you would have to be feeling really rough to pass up a holiday to the paradise island of Mustique, but there will be few excuses left for avoiding royal engagements when Kate gets home.

Yes, Kate and William have shrugged off any lingering worries about morning sickness (Sorry! Hyperemesis gravidarum!) and jetted off for what is fast becoming an annual tradition - a few days in the sunshine of the Carribean Island famed as the playground of the rich and royal ever since Princess Margaret courted Roddy Llewellyn on its shores, and the gangster John Bindon perfomed obscene party tricks for her pleasure involving half a dozen beer glasses.

The trip involves an eight-hour flight folowed by a hop in a sick-making light aircraft, so lets hope Kate has packed the lavender shortbread.

Spokesmen for the young royals are refusing to confirm their whereabouts, but the Sun quotes a source: “The Duke and Duchess have joined the Middletons for a winter break. Both William and Kate were hoping her condition would not stop her from making the eight-hour flight to Barbados and the connection to Mustique. A month ago such a journey would have been unthinkable for her, so this is a clear sign she has made a virtual recovery.”

It is doubtful how well the taking of an exclusive holiday by the young royals will play in a particularly cold and depressing British winter, so soon after the public were being told that Kate was so ill with morning sickness (Sorry! Hyperemesis gravidarum!) that she could scarcely be expected to attend any more public events or perform public duties for the months ahead.

But a winter trip to Mustique is something of a Middleton family tradition, and William has made a habit of joining them in recent years. This is Will and Kate’s seventh trip to Mustique together.

Last year they stayed at a fully staffed villa, Aurora House, which belongs to hedge-fund manager Mark Cecil, who along with his wife, Katie, was a guest at the royal wedding.

The patronage of the young royals is a coup for the Mustique Company, the private corporation that effectively owns the island, reviving the exclusive royal association with Princess Margaret, which did a great deal to make the word “Mustique” a byword for glamour and hedonism in the 1960s and '70s. In recent years the island has hosted holidaymakers such as Mick Jagger, Amy Winehouse, and Bill Gates, but an endorsement from a fresh generation of superstar royalty will do much to recall the island’s heyday.

Mustique is also famous for the omertà that ensures that very little celebrity tittle-tattle ever makes it off the island. The Mustique Company boasts that it is “dedicated to protecting the island’s privacy.”

As in previous years, the island will be more or less locked down for the latest royal visit, and other guests at the Caribbean hotspot will likely face a range of strictures to protect the Middletons’ privacy, including a ban on using the souped-up golf buggies (or “mules”) that are the main form of transport on the island. Guests will instead probably be required to be driven by taxi for the duration of the royal visit, ensuring that they can’t get near the Middleton compound without an invite, something that has irritated regulars in the past.

Don't expect to see any pictures. The chances of any mistake being made by the Mustique Company - of the type that might allow photos of the duchess sunbathing topless for example - to emerge from the trip are remote.