A woman who is a known stalker of Prince Harry came close to the son of King Charles on two occasions during his recent visit to Britain, a security source with knowledge of the incidents said.

The incidents occurred during the four-day trip by King Charles' son last month, once at a charity awards event and also when he visited the Centre for Injury Studies (CIS), part of Imperial College London.

According to the Telegraph newspaper, the woman was known to Harry's staff as she was on a list of fixated individuals drawn up by a private intelligence company for his personal protection team. She has previously followed him to Nigeria, the paper said.

"These incidents are not uncommon for members of the royal family," the security source said.

"It differs, however, because there was no police presence or close protection — it was left to two staffers from his private office to intervene. This time they got lucky, recognising the fixated individual. Relying on luck is not a long-term fix."

A spokesperson for Harry declined to comment while police say they do not discuss security arrangements.

In May, Harry lost a high-profile court battle with the British government over a decision to strip him of automatic police protection while in Britain.

During court hearings, the government's legal team said a bespoke arrangement for the prince had positive advantages from a security assessment point of view.

However, the security source said that as the son of the monarch and "one of the most famous people in the world", it felt like there was "an inevitable foreboding looming over this whole issue".

Neil Basu, the former head of the UK's counter-terrorism police, told the Telegraph that fixated individuals posed the greatest threat to the royals.

"The only way of stopping those kinds of people is to be close to the principal and to smother them if they get approached," he said.