There's nothing like a royal baby to lift a nation's spirits -- and those of its retailers, who are hoping to cash in on Prince William and Catherine's new arrival this month.

It wasn't long after the pregnant Duchess of Cambridge was admitted to hospital with morning sickness in December that one enterprising designer starting selling royal sick bags.

But that was just the beginning.

With the new heir now expected within days, retailers have put a royal spin on everything from biscuits to books and have stocked up on commemorative mugs, key rings and plates.

Even Kate's parents appear to have got in on the act -- the Middletons' Party Pieces online business is showcasing as 'new' a range of "I'm a Princess" party cups, plates and napkins.

There is no shortage of baby products with a royal theme, from leading British firm Mothercare's romper suits for a "Prince in Training" to blankets and even dribble bibs adorned with crowns.

If they aren't to your taste, one company has published a book of sewing patterns for traditional bonnets, booties and christening gowns suitable for a future monarch.

The upmarket London hotel, Grosvenor House, has taken it further with a bespoke nursery suite designed "with a royal baby in mind" by the boutique that furnished William's childhood bedroom.

Costing £2,300 ($3,550, 2,700 euros) a night, the rooms contain handcrafted and painted furniture, including a crib equipped with a regal coronet and canopy.

The ivory colour scheme may be impractical for babies, but for that kind of money, you would hope someone else would clean up.

Unlike the Olympics, a highly lucrative brand that is fiercely protected by the International Olympic Committee, anyone with an eye for a marketing opportunity can use the royal name.

And the new baby, like the queen's jubilee last year and the royal wedding in 2011, offers a welcome boost for an industry still suffering the fallout of the global economic crisis.

"These kind of events lead to a temporary feel-good lift. It will really help to boost particular brands and products," said Mandy Murphy, a spokeswoman for the British Retail Consortium.

The Centre for Retail Research (CRR) estimates that £199 million ($297 million, 231 million euros) were spent in Britain on souvenirs and merchandise produced for William and Kate's wedding at Westminster Abbey.

Among the memorabilia was a tea-towel bearing the couple's faces, which William's Royal Air Force (RAF) colleagues bought and made him use while he was washing up in the mess.

The CRR predicts £80 million will be spent this year on royal baby toys and products, and £76 million on books, DVDs and other media related to the royal family.

Publishers have rushed out a slew of children's books about fictional pregnant princesses, the newborn's crying that might wake up the queen, and even a history of the diapers used to cover royal babies' bottoms.

Mills & Boon, the romance fiction series, has a special release unimaginatively entitled "Royal Baby", with the tagline: "The prince demands an heir... and what he wants, he gets!"

With an eye to those inevitable sleepless nights, several albums are on sale promising to soothe even the most fractious royal heir with classical music and traditional lullabies.

Given that 31-year-old William normally listens to hip-hop and dance music, Kate might consider one of those for herself.

New mums are advised to keep up their energy levels and the duchess might also enjoy the various tins of biscuits on offer in the shape of royal rattles, baby bottles, booties and prams.

Of course it wouldn't be a royal occasion without a celebration mug, although retailers are holding back until they know if the baby is a girl or a boy -- something William and Kate themselves apparently do not yet know.

They will not want to make the same mistake as the Chinese manufacturer which rushed out wedding mugs after William got engaged and accidentally used a picture of his brother, Harry.