Meghan Markle has been warned by an expert to "get out now" of her ongoing privacy case.

The Duchess of Sussex is suing the Mail on Sunday's publisher Associated Newspapers (ANL) over the publication of parts of a handwritten letter sent to her father Thomas Markle in August 2018.

Meghan is seeking damages for alleged misuse of private information, breaching the Data Protection Act and infringement of copyright over five articles published in February 2019 which included extracts from the "private and confidential" letter to her father.

The newspaper claimed in court documents that the duchess has "compromised" any expectation of privacy in relation to the letter by allowing details of her private life to be published in a recent biography.

The Duchess of Sussex is suing the Mail on Sunday over parts of a handwritten letter sent to her father

Now Mark Stephens, of British firm Howard Kennedy, said Meghan risks experiencing an even greater invasion of privacy while the legal battle continues.

He told Newsweek: "If I was advising Meghan I'd be saying get out now.

"This is another hole below the waterline.

"The risk is that how she curates her reputation, what she allows into the public domain and what she doesn't, are now things that will be picked over by lawyers in cross-examination.

"The stakes are enormous because at the moment her reputation is not damaged particularly.

"She's had an invasion of privacy and she feels strongly about it but the reality is she has only got a downside here.

Meghan with her father Thomas

"The more that she protests about wanting to protect her privacy, the more that people are going to investigate how she has curated the Streisand effect of amplifying the positive PR and negativizing the other PR."

The Streisand Effect, named after singer Barbra Streisand, is an online phenomenon in which an attempt to hide or remove information such as a photo results in the greater spread of the information in question.

ANL was this week given permission to rely on a recent biography of the Duke and Duchess of Sussex - Finding Freedom by Omid Scobie and Carolyn Durand, which was published in August - in its written defence to Meghan's High Court claim.

In its amended defence, seen by the PA news agency, the publisher claims Meghan "compromised" her right to privacy in relation to the letter as she "permitted information about her own private and family life and relationships, correspondence, as well as the private lives of other people, to enter the public domain by means of the book".

ANL argued that the account in Finding Freedom of Meghan's letter to her father and his response is "very critical of Mr Markle", while the Sussexes are portrayed as "generous, thoughtful and considerate".

Meghan Markle is suing Associated Newspapers Ltd

Antony White QC, for ANL, said in the document: "It is to be inferred that this account of the letter is part of the version of events that the claimant wanted published; that she caused this account to be given to the authors for the purpose of publication; and that, had the defendant published this version of events - that is, an account entirely from her point of view - the claimant would not have had or made any complaint about the publication of any of the contents of the letter."

The barrister added that Finding Freedom "accurately reflects the claimant's own intent and purpose in bringing this claim, which was to complain of the content of the articles and other articles published by the defendant that she finds objectionable because they are not wholly favourable to her and try to prevent any such further articles".

The updated defence also denies that Meghan "has been caused any distress, damage, humiliation or embarrassment" by the publication of the letter to her father.

On Tuesday, Judge Francesca Kaye allowed ANL to amend its defence to Meghan's claim in order to rely on Finding Freedom and argue that the Sussexes "co-operated" with its authors.

Thomas Markle

Meghan's lawyers have described the accusations that the duke and duchess "collaborated" with the authors as a "conspiracy theory", saying references to the letter in the book were simply "extracts from the letter lifted from the defendant's own articles".

In separate witness statements filed on behalf of the duchess, Mr Scobie said "any suggestion that the duke and duchess collaborated on the book is false", while Meghan's solicitor Jenny Afia described much of the information about the Sussexes in Finding Freedom as "extremely anodyne", "the product of creative licence" or simply "inaccurate".

The duchess' legal team are likely to file a written response to ANL's amended defence in the coming weeks, but may also challenge the decision to allow the publisher to amend its defence at the Court of Appeal.

Meghan's case against ANL, which has been listed for a 10-day trial in January, is one of several High Court claims recently brought by the duke and duchess against media organisations.

Meghan is also suing the Splash News and Pictures Agency over "long-lens" photographs of her and her son Archie taken in a Canadian park in January this year.