Dubai's ruler Sheikh Mohammed bin Rashid al-Maktoum ordered the phones of his ex-wife and her lawyers to be hacked as part of a "sustained campaign of intimidation and threat" during the custody battle over their children, England's High Court has ruled.

Sheikh Mohammed used the sophisticated "Pegasus" software, developed by Israeli firm NSO for states to counter national security risks, to hack the phones of Princess Haya bintal-Hussein, half-sister of Jordan's King Abdullah, and some of those closely connected to her, according to the rulings.

Those working for him also tried to buy a mansion next door to Princess Haya's estate near the British capital, intimidatory action the court ruled that left her feeling hunted, unsafe and like she "cannot breathe anymore".

The latest rulings come 19 months after the court concluded that Sheikh Mohammed had abducted two of his daughters, mistreated them and held them against their will.

"The findings represent a total abuse of trust, and indeed an abuse of power to a significant extent," Judge Andrew McFarlane, President of the Family Division in England and Wales, said in his ruling.

The sheikh had denied the allegations of hacking and his lawyers had argued other countries in the Middle East could have been to blame.

"The father has no knowledge of any such activity taking place," David Pannick, his lawyer, told the court. "He has not authorised it or instructed, encouraged or in any way suggested any other person should use NSO or any software in this way."

Sheikh Mohammed, 72, and Princess Haya, 47, have been involved in a long, bitter and expensive custody battle since she fled to Britain with their two children, Jalila, 13, and Zayed, 9.

She said she feared for her safety amid suspicions that she had had an affair with one of her British bodyguards.

Among those targeted by the hacking was Princess Haya's lawyer Fiona Shackleton, a member of Britain's House of Lords who represented British heir-to-the-throne Prince Charles in his divorce from his late first wife Princess Diana.

The activity came to light in August last year after Ms Shackleton was urgently tipped off by Cherie Blair, the wife of former British Prime Minister Tony Blair, that she and Princess Haya had been hacked, the court was told.

Ms Blair is also a prominent lawyer who worked as an external adviser for NSO.

At the same time a cyber expert from the University of Toronto's internet watchdog Citizen Lab, which researches digital surveillance, also alerted Haya's lawyers after tracking the hacking, the court heard.

Once the hacking was uncovered, NSO cancelled its contract with the UAE, Princess Haya's lawyers said.

The Israeli firm said it could not immediately comment on the case but said it took action if it received evidence of misuse of Pegasus.

Ms Shackleton and Ms Blair declined to comment.

Mohammed is regarded as the visionary force behind Dubai's ascent into a global commercial hub. He has sought to burnish the Gulf city's reputation on issues such as human rights and equality.

There is no indication that last year's ruling caused any major damage to him personally or to the UAE.

Last month Britain and the UAE announced a "new, ambitious Partnership for the Future" involving billions of dollars in trade and investment.

Reporting restrictions on the judge's findings after a year of hearings were lifted today.

"I do not feel that I can move freely forward as things stand now, while I am and feel hunted all the time, and I am forced to look over my shoulder at every moment of the day," the British-educated princess said in one witness statement.

The legal costs of the case have run into millions of pounds, with the case involving some of Britain's most prominent lawyers. The costs of one appeal alone was cited by the court as costing £2.5m.

The sheikh, who is vice president and prime minister of the United Arab Emirates, initially sought to have the children brought back to Dubai, but has since suffered repeated defeats in the English courts.

In a judgment released today, Judge McFarlane ruled that the children should live with their mother.

In a ruling published last March, the judge concluded that Sheikh Mohammed had subjected Princess Haya to a campaign of intimidation which made her fear for her life.

He concluded the sheikh had arranged for his daughter Shamsa, then aged 18, to be kidnapped in 2000 off the streets of Cambridge in central England and flown back to Dubai.

The judge also found it was proved that Mohammed had arranged for Shamsa's younger sister Latifa to be snatched from a boat in international waters off India by Indian forces in 2018 and returned to the emirate.

While his findings do not amount to a determination of criminal guilt, they mean Judge McFarlane is satisfied the allegations are proven on the balance of probabilities and that this may impact arrangements for contact with his children in the future.

"As the previous findings of fact establish, the father, who is the head of government of the UAE, is prepared to use the arm of the state to achieve what he regards as right," he said.

"He has harassed and intimidated the mother both before her departure to England and since. He is prepared to countenance those acting on his behalf doing so unlawfully within the UK."