Camped outside St Mary's Hospital in London, eccentrics decked out from head to toe in Union Jack colours are counting down to the latest addition to Britain's royal family.

"Diana superfan" John Loughrey cannot hide his excitement, dancing a jig and singing on the pavement.

"Get down here, you're missing something, the atmosphere is electrifying," he said, as hospital patients and staff hurried past, grinning.

"Once the baby is born we will be celebrating! We will be dancing for two hours!" he told AFP.

"This is what you call Shakespeare, this is theatre!"

The same loyal fans all came to the same clinic in 2013 for the birth of Prince George, the first child of Prince William and his wife Kate.

Two years later they are back to witness the birth of George's little brother or sister.

Around a dozen of them could be seen on Friday, preparing to spend a fifth night sleeping in two small two-person tents and on nearby benches.

Among them is Terry Hutt, the famous "Union Jack Man" who at 79 is still a feature at all royal events.

"It's important for me," he told AFP, wrapped in a sleeping bag donated to him by a television channel.

"Someone stole my sleeping bag. Unfortunately that night was freezing," he said, fixing his hat covered in Kate, Diana and Queen Elizabeth II badges.

Next to him are two beaming William and Kate impersonators, posing for a Japanese television station holding a plastic baby doll.

"I'll stay until the baby is born, we are betting on the weekend, Sunday would be nice," said Kathy Martin, another loyalist originally from Australia.

Loughrey added: "The whole world wants a girl, and I'm sure William and Catherine too.

"The baby is gonna have great fun together with little George. But I still think that Prince George secretly wants to be the boss," he laughed.

Unlike two years ago, when the world's media remained camped outside the maternity wing for three long weeks, the scene is much calmer this year.

Journalists have deliberately been kept away until Kate is admitted to the hospital in labour and even the royalists admit there is less of a frenzy.

"It's different this time for the simple fact that baby George came first," said Gianni de Capitani, an Italian man who said he moved to London when William, 32, "was five months old". AFP