The former chief executive of JNF UK, who is in legal dispute with his ex-employer - and is also suing this newspaper over its reporting of his departure - this week took one of Britain's top law firms to court in a separate action which has brought extraordinary revelations about the charity.

Simon Winters, who left the charity two months ago following the arrival of new chairman Samuel Hayek, is seeking an injunction to stop Mishcon de Reya acting for JNF in his dispute with it over the end of his employment, alleging a conflict of interest.

Before a High Court judge on Wednesday, Mr Winters claimed that Mishcon and one of its partners, Anthony Julius, had previously acted for him in various matters and received confidential information after he had "poured his heart out" to Mr Julius.

One of the matters concerned a threat by Mr Winters to sue the committee of Glasgow's JNF for defamation two years ago.

His counsel, Alastair Wilson QC, told Mr Justice Henderson that Mr Winters was therefore "astonished" when he received a letter from Mishcon in June informing him that he had been suspended from his post amid "allegations in his role as chief executive".

The court was told of:

An acrimonious split with its former Israeli partner that cost £4 million in legal fees;

How JNF tracked down the person responsible for leaking documents to the JC from a 108-page dossier of allegations made against Mr Winters in relation to expenses claims;

Claims that the office of new chairman Samuel Hayek was bugged.

Mr Wilson told the court that the case had its origins in the bitter dispute that started in 2005 between JNF and its Israeli counterpart, Keren Kayemet Le'Israel, which was settled in February this year.

The legal actions cost the charities an estimated £4 million. It also led to a split in JNF UK, with its Glasgow branch supporting KKL and leaving the main organisation.

The situation also prompted the creation by some JNF employees of what Mr Wilson called a "deeply disloyal dossier containing a number of apparently very serious allegations about his conduct as chief executive".

The dossier was not passed to the charity's trustees, and "festered" until February 2006, when it was passed to another employee, Harvey Bratt, and then to a vice-president, Jeffrey Zinkin. Within days, it was discussed at a meeting of the trustees and, as a result, Lee & Allen, a firm of forensic accountants, was called in to carry out a thorough investigation "which exonerated Mr Winters completely".

"In the meantime," said Mr Wilson, "a rather unpleasant thing was happening. Letters were being sent to the Jewish Chronicle and the Jewish Telegraph containing allegations taken from the dossier."

Mr Wilson said the letters were sent via e-mail under the pseudonym of "Anthony Jacobs".

To discover the identity of the culprit, Mishcon made a court application naming both JNF and Mr Winters to force an internet service provider to reveal the name. JNF settled the bill for this.

The person sending the letters was revealed as Mark Lovatt, son of then JNF vice-president Stanley Lovatt, the force behind the Glasgow JNF committee.

Mr Julius advised JNF to take no action against the Scottish committee but Mr Winters decided he would go ahead, said Mr Wilson. It was Mr Winters's case that the lawyer had dictated the substance of a letter, threatening legal action, over the phone. The letter was subsequently sent to the entire Glasgow JNF board, threatening to sue them for defamation.

"We say that Mr Julius' approval and amendments [that he made] to the letter couldn't be any clearer indication that he was acting for Mr Winters personally," said Mr Wilson.

In a statement, Mr Winters said he had found Mr Julius supportive and that the solicitor was "happy" to act for him after he had been exonerated. He said it was important that "someone of Mr Julius's stature" would act for him.

In September 2006, another investigation was launched, this time by the Charity Commission after chartered accountant David Lewis sent them a copy of the dossier. But again, it found no wrongdoing and Mr Winters was cleared again, said Mr Wilson.

Now, Mr Wilson continued, "the position is that Mr Winters has been threatened by Mishcon with dismissal for misconduct and another firm of forensic accountants is to look at the doings of the JNF, in particular to consider the position of the chief executive".

In another witness statement, Mr Winters said he was being "squeezed" by Mr Hayek and his functions taken away. He sent a solicitor's letter to JNF saying he had been constructively dismissed because of the new chairman's behaviour.

"He was astonished to receive a reply from Mishcon saying there was another investigation into him. It said he had been suspended by a JNF management team in connection with allegations in his role as chief executive," said his counsel.

There was also an allegation, said Mr Wilson, that Mr Hayek's office had been bugged. But the bugging equipment, according to his client, had nothing to do with the new chairman; it had been partly dismantled when Mr Hayek arrived and was being stored in a cupboard.

"Mr Hayek was never bugged," said Mr Wilson. "This is a clear case where the solicitor has changed sides where my client is concerned," he added.

Later, Justin Fenwick QC, for Mishcon de Reya, sought to establish that it and Mr Julius were acting for JNF but not at any time for Mr Winters personally.

He put it to Mr Winters, in the witness box, that all the time he claimed he was talking confidentially to Mr Julius, the lawyer and the company were in fact acting on behalf of JNF.

Mr Fenwick said: "You, as chief executive, expected them to act in the best interests of the JNF."

Mr Winters: "Broadly speaking, yes."

Mr Fenwick: "Do you agree that at least the vast majority of your interaction with Mishcon and Anthony Julius was in relation to the affairs of JNF?"

Mr Winters: "Yes, I would agree."

As the JC went to press, Mr Winters' evidence was continuing. The case was expected to conclude today (Friday).