The Duke of Sussex gave Russian hoaxers his personal email and phone number and even rang them back on his mobile, it has been claimed.

Prince Harry responded to an email sent by Vladimir Kuznetsov and Alexey Stolyarov, who told the Sun that none of his advisers checked if they were genuine.

The claim further highlights lapses in security and screening for the Sussexes as they leave the protection of Buckingham Palace officials to go it alone in North America. It also illustrates how easily Harry, and Meghan’s Hollywood PR team, were duped, and the lack of any stringent checks.

During two calls, said to have been made on New Year’s Eve and 22 January, Harry allegedly believed he was talking to the Swedish climate change activist Greta Thunberg and her father.

In the calls he spoke about the couple’s decision to step back from royal life, criticised the US president Donald Trump as having “blood on his hands” over his climate change credentials, and elaborated on his battle with a tabloid media he believed was trying to “sink” him and Meghan.

He apparently failed to spot he was being pranked as he offered help in relocating penguins, native to the South Pole, to the North Pole. The hoaxers, known as Vovan and Lexus, also tricked him into believing mining companies close to Trump were exploiting the fictional island of Chunga-Changa.

Revealing the anatomy of the hoax on Thursday the Sun, which first reported the details, said the hoaxers had posed as Thunberg’s “director” using a fake email address set up under the name of Ueli Maurer – the then president of Switzerland.

Under the heading “Call or meeting with Greta Thunberg” they sent emails to Harry and to Meghan’s Hollywood PR team at the beginning of December. Harry then used his personal email address to reply on 29 December, when the couple were at their rented mansion on Vancouver Island, the newspaper said.

On 20 January, Harry said to have also replied to “Greta” via the Ueli Maurer address, believing she was in Davos, Switzerland, meeting world leaders.

It was claimed Harry rang the hoaxers on his mobile without withholding his number.

Stolyarov told the Sun: “His staff must have forwarded him the email. Probably the emails were transferred through many people before he got it. We were shocked when he emailed us. No one ever checked us out to see who we really were.”

A spokeswoman for the Sussexes declined to comment when asked if there was any doubt the voice in the audio was that of Harry. There was also no comment on the security issues the hoax has raised,

The Queen’s former press secretary Dickie Arbiter said on Wednesday: “As long as Harry and Meghan are over there, they’re out of the protection of the system.

“For all its faults, the system does, and is there, to protect. If you’re out of the system you’re open to anything and everything”.

The couple jave not revealed details of staff at their Canadian home. Their 15-strong team at Buckingham Palace is due to be disbanded on 31 March when the couple step back, with some being made redundant and others redeployed within the royal households.