A decision may not be made for weeks on whether to allow a case involving an Israeli conflict resolution expert to go to a full trial, a judge has warned.

Moty Cristal is seeking damages totalling £26,500 and an apology from Manchester Mental Health and Social Care Trust after it cancelled a workshop he was due to run for its staff last year.

A pre-trial hearing last week was told that the invitation to Professor Cristal to run the training session was withdrawn by the Trust after members of the Unison trade union threatened to boycott it because he was Israeli.

But Judge David Mitchell told Central London County Court that the complexity of the case meant its future in the courts was unclear.

Following three days of legal arguments, Judge Mitchell told lawyers that it would “take a lot of thinking through” before he could rule on the next steps.

He said: “The easy solution is to allow the thing to run and then fight it out. The problem we find with claims like this is that if we don’t ensure proper legal boundaries they run out of all control. They take disproportionate amounts of time and our resources.”

Judge Mitchell told Dinah Rose QC, acting for Prof Cristal, that he was “not against” her, but that he was “concerned” by the number of legal issues the sides were debating and feared the case would “simply mushroom into a huge series of issues”.

The judge added a further warning that with appeals likely from both sides, it may end with the case going as far as the Supreme Court.

“I have a lot of work to do on it. Nothing I say must be construed as me having made up my mind. When the arguments are over, that’s when the judges go to work,” Judge Mitchell concluded.

He pledged to publish a judgement “as soon as I can”.

The case partly focuses on the interpretation of the phrase “Israeli negotiator”. Prof Cristal claims that the Trust’s use of the term was an indication that the event had been cancelled because of his nationality. But Unison’s lawyer Christopher Jeans QC told the court it was “extraordinary” to interpret the phrase that way.

The union would defend the claim on the basis that its members’ objection to Prof Cristal was because he had in the past been a negotiator on behalf of the Israeli government.

There was “plainly an alternative interpretation” of “Israeli negotiator”, said Mr Jeans. Unison had no prejudice against people of any nationality and regularly campaigned for equality, he added.

The court had earlier heard that the Trust’s lawyers would argue that Prof Cristal’s claim was “trivial” and that the cost of the litigation was out of proportion with the benefits that he could gain.