Billionaire Elon Musk has added a severance payment made by Twitter to a whistleblower to the list of reasons he feels entitled to walk away from his €43.33 billion deal to buy the social media platform.

A termination letter sent to Twitter accused the firm of not informing him about a multi-million dollar severance payment it made in June to departing security chief Peiter Zatko.

Mr Zatko went on to file a whistleblower complaint criticising Twitter's security practices, according to a copy of the letter filed with the Securities and Exchange Commission.

Mr Musk's lawyers argued that failing to seek his consent before paying Mr Zatko provides another legal basis to break the merger deal with Twitter, but Twitter disagreed.

"My friend seems to be arguing that Twitter should have gratuitously told Musk that there existed a disgruntled former employee who made various allegations that had been inquired upon and found to be without merit," Twitter attorney William Savitt said earlier this week.

"That doesn't make any sense."

Twitter did not respond to a request for comment yesterday.

Mr Musk said in his original termination letter that he was cancelling the deal because he was misled by Twitter concerning the number of bot accounts on its platform, allegations that were rejected by the company.

In a mixed ruling earlier this week, chancellor of the Delaware court Kathaleen McCormick, who is overseeing the case, said Mr Musk could add whistleblowing revelations from Mr Zatko that surfaced in August.

Peiter Zatko filed a whistleblower complaint

She denied his request to push back the litigation, saying prolonging "would risk further harm to Twitter too great to justify".

Mr Musk has been locked in a bitter legal battle with Twitter since announcing in July that he was pulling the plug on the purchase of the company.

The five-day trial is due to begin on 17 October in Delaware.