Buckingham Palace is to investigate allegations of bullying against the Duchess of Sussex by former royal staff, it announced on Wednesday, as relations between members of the royal family appeared to descend to new lows.

In a highly unusual statement, the palace said it was “very concerned” by a report in the Times of claims that Meghan had driven out two personal assistants during her time as a working royal, while Kensington Palace staff had been “humiliated” on several occasions.

It came hours after sources close to Meghan and Prince Harry suggested that the emergence of the bullying allegations was timed to undermine their forthcoming interview with Oprah Winfrey.

The source acknowledged that a direct accusation of responsibility against the palace by the couple had been clumsily phrased, but suggested “people in the royal orbit” were responsible for the timing of the story – and claimed it was intended to create scepticism over Meghan before the high-profile interview to be aired on Monday.

In a statement, Buckingham Palace said: “We are clearly very concerned about allegations in the Times following claims made by former staff of the Duke and Duchess of Sussex.

“Accordingly our HR team will look into the circumstances outlined in the article. Members of staff involved at the time, including those who have left the household, will be invited to participate to see if lessons can be learned.

“The royal household has had a dignity at work policy in place for a number of years and does not and will not tolerate bullying or harassment in the workplace.”No timetable has yet been set out for the investigation but the hope was to start soon, sources indicated.

The Times had reported that a complaint was made in October 2018 by the Sussexes’ then communications secretary, Jason Knauf, which alleged Meghan’s behaviour had driven two personal assistants out of the household.

Lawyers for Harry and Meghan told the newspaper it was “being used by Buckingham Palace to peddle a wholly false narrative” about Meghan’s behaviour. Knauf is now chief executive of the Duke and Duchess of Cambridge’s Royal Foundation, the primary charitable vehicle for William and Kate.

A source close to Harry and Meghan said that a separate allegation – that Meghan had worn earrings that were a wedding gift from the Saudi crown prince Mohammed bin Salman shortly after the murder of the journalist Jamal Khashoggi – had been misrepresented but was “embarrassing”.

The recriminations over the claims underline the depth of tensions to emerge since the couple’s decision to step back from their role as working members of the royal family last year. They also reflect the chasm between Harry and his brother, the Duke of Cambridge, since the brothers divided the staff they once shared, particularly in their communications team.

The timing of the story will also be seen as a marker of the high stakes of the Oprah interview. The conversation, in which Harry and Meghan will discuss their lives within the royal family and their exit from their roles, has been trailed as “intimate” and “wide-ranging”. On Wednesday ITV said it would show the interview in the UK on Monday night, 24 hours after the two-hour special is broadcast in the US.

The Times reported that a complaint was made in October 2018 by Knauf, then the Sussexes’ communications secretary, which alleged Meghan had driven two personal assistants to leave the royal household and was undermining the confidence of a third staff member. It was reported that he handed in his notice the following month.

In 2019, Knauf – who had advised William and Kate, and Harry and Meghan, on media relations – took up a role focusing only on William and Kate.

Knauf was reported to have emailed Simon Case, who was then William’s private secretary and is now the cabinet secretary at Downing Street, after discussions with Samantha Carruthers, the head of HR. Case was said to have forwarded the email to Carruthers, who was based at Clarence House.

Knauf reportedly said Carruthers had “agreed with me on all counts that the situation was very serious” and he remained concerned that nothing would be done.

The Times reported that lawyers for Harry and Meghan had told the newspaper that it was “being used by Buckingham Palace to peddle a wholly false narrative” before the Oprah interview.

A spokesperson for the couple was quoted as saying: “Let’s just call this what it is: a calculated smear campaign based on misleading and harmful misinformation. We are disappointed to see this defamatory portrayal of the Duchess of Sussex given credibility by a media outlet.

“It’s no coincidence that distorted several-year-old accusations aimed at undermining the duchess are being briefed to the British media shortly before she and the duke are due to speak openly and honestly about their experience of recent years.”

The royal household will be braced for revelations from the Oprah interview. The bulk of the programme will be a conversation with Meghan. Harry is expected to join only for a concluding, future-oriented segment.

The couple confirmed last month that they were expecting a younger brother or sister for their one-year-old son, Archie.

It come as Harry’s grandfather, the Duke of Edinburgh, is ill in hospital in London. Prince Philip, 99, spent nearly two weeks in the private King Edward VII’s hospital before being transferred to St Bartholomew’s hospital on Monday. On Wednesday, Camilla, the Duchess of Cornwall, said his condition had “slightly improved”.