Children of millionaire inventor demand their step-siblings are cut out of his £5.4m will, claiming their late father didn't understand what he was doing when he split his fortune between his two families

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The children of a helicopter-loving, multi-millionaire inventor are locked in a High Court fight over who inherits his £5.4 million fortune after they demanded their step-siblings were cut out of the will.

Dr Jack Leonard was a genius engineer who developed an early foetal heart rate monitor, before going into business and later training as a helicopter pilot.

He was married twice, having four children with first wife Audrey Leonard and later treating 'as his own' the family of his second wife Margaret Leonard - who he flew in his chopper to meet on their first date.

When he died, aged 87, in 2019, he split his fortune roughly seven ways between his two families.

But the families are fighting over Jack's final will, with his children Megan, Sara, Jonathan and Andrew Leonard saying their father's step-children should be cut out because he didn't understand what he was doing.

Dr Jack Leonard was a genius engineer who developed an early foetal heart rate monitor

Sara Leonard is arguing with her three siblings that  her step-siblings should be cut out of the will

They insist that their father wanted them to get his fortune and, in his final years, he did not have the capacity to understand the will which he made.

His step-children on the other hand argue that by the time of the second will he had been married to his second wife for 16 years, was extremely close with her children and was assessed as having 'testamentary capacity'.

Giving evidence, Sara Leonard - who with Megan had been a director in their father's flying school company - told Mrs Justice Joanna Smith that their fight against the will was not about money, but doing the right thing.

'It's a point of principle,' she said. 'I don't think the 2015 will is one my father had capacity to make.'

But Margaret's children - glazing company boss Mark Smith, 66, and yoga teacher Elizabeth Leslie, 57, - say they and the children of their deceased sister Melanie Turner were rightly included because of the close bonds they had formed with Jack after he met their mother.

Jack Leonard was a talented engineer, who co-founded Eurotherm International, a Worthing-based business which became a world leader in the supply of temperature control devices to industry.

The Manchester-born engineer began his career in Edinburgh, where he developed a foetal heart monitor, before going on to found Eurotherm with colleagues in 1965.

The business was a huge success, turning over £1m by 1970, when Dr Leonard temporarily moved his young family to Virginia, in the US, to take the company global.

Megan Leonard, who along with Sara had been a director in their father's flying school company, outside the High Court

Elizabeth Leslie, 57, a yoga teacher, is arguing with her siblings that her stepfather did have the capacity to make his 2015 will

Outside of his business life, Jack was passionate about aviation, trained as a helicopter pilot and set up Fast Helicopters, a flying school and tour company in Worthing.

He married first wife Audrey in 1958 after meeting her at Manchester University and they had their children Sara, 60, former pub manager Megan, 53, and US-based Andrew and Jonathan.

Audrey died in 1998 and, the court heard, Jack very soon afterwards started using an internet dating service, something which Megan told the court was a 'concern' for the family.

He met Margaret through the dating service and their first meeting was on her 62nd birthday at Southend Airport, said his step-children's barrister, Thomas Dumont KC.

'Jack flew in on his helicopter, wearing his pilot's epaulettes,' he told the judge.

'Jack swept Margaret off her feet. They were married a year later on 7 November 1999, Jack aged 68 and Margaret 63. Margaret adored Jack, and he was devoted to her.'

They lived together in West Sussex and latterly a £1.1million house in Hutton Place, Brentwood, Essex.

They enjoyed a 'very good standard of living,' travelling the world together and even flying for meals at hotels around the country in his helicopter.

Mr Dumont said there was an 'extraordinary close, loving and devoted relationship Jack shared with Margaret and her family.'

With Margaret's grandchildren, he stepped into the 'role of grandfather in all but name, attending sports days, school plays, and taking an active interest in their academic lives and hobbies,' he said.

But he continued: 'Jack's relationship with his own children, and indeed Margaret's relationship with them, was different.

'This in part is no doubt due to the fact that Jonathan and Andrew lived in the US, Megan lived in Bolton and Sara in Teddington, some distance from Jack and Margaret's home initially in West Sussex, but subsequently in Essex.'

Sara, Megan and Andrew had not spoken to Margaret during Jack's funeral and wake, and she had not been mentioned in Sara's eulogy, the barrister said.

The court heard Jack had made a will in 2007, leaving his share of their home to Margaret, with the most of the rest split roughly five ways between Margaret and his own children.

Mark Smith outside the High Court after hearing in dispute over his step-father Jack Leonard's will

However, he then made the disputed October 2015 will, which left the Brentwood house to Margaret and the rest of his estate on trust for her for life.

It would only be on her death that his children would get their inheritance, but they would also have to share it seven ways with their step-siblings Mark and Elizabeth, with Jack's deceased stepdaughter Melanie's children getting her share.

The decision sparked a High Court battle in London, with his four children now trying to have the will overturned, claiming he did not have capacity to make it when he did.

Their barrister, Constance McDonnell KC, said there were 'obvious alarm bells' as to whether the ailing aviator had capacity to understand what he was doing in 2015.

He had dementia and had suffered a suspected stroke, while the will had been prepared not by a trained solicitor but a tax advisor, without the usual precautions to make sure he was mentally fit.

'Jack's cognitive difficulties would have been less apparent to an untrained observer and, to an extent, he was able to maintain a social facade, particularly in certain social or family settings,' she said.

She said Jack had a 'consistent and longstanding wish' that most of his wealth would ultimately pass to his own four children, which was shown by his making of the 2007 will eight years into his marriage to Margaret.

'It would have been inconsistent with Jack's settled intention, when capable, to divert his own wealth away from his children, other than to the extent he felt it appropriate to provide for Margaret herself,' she said.

'His 2007 will reflected his settled intentions.'

She said that, by 2015, Jack had already 'provided generously' for Margaret and knew she would have more than enough to enjoy the same standard of living after his death.

'At no time did Jack suggest to anyone that he felt any moral duty to provide in his will for any of Margaret's children or grandchildren,' she continued.

'There is no record in the 2013-15 will file of any explanation from Jack to support any alleged intention for Margaret's family to inherit any of his wealth.'

There was also no evidence of the will being explained to Jack in the months leading up to its signing and he 'could not have understood it merely by reading it to himself.'

'There is no evidence that he did in fact read it,' she added.

But for Jack's step-family, Mr Dumont said a proper analysis of the will-making documents showed that Jack did have 'testamentary capacity' in 2015.

There was also good reason why he would have wanted to benefit Margaret's children alongside his own, he told the judge.

'By the time the 2015 will was executed, Jack had been married to Margaret for around 16 years,' he said.

'They adored one another. He had become an intimate member of Margaret's family.

'He had 'done life' with them, sharing in the family's celebrations and in their moments of grief. He was grandfather in all but name to her grandchildren, and a great-grandfather to her great-grandchildren.

'Nothing could be more natural than Jack wanting to provide first and foremost for Margaret. Nor should it be in the slightest bit surprising that, given his close relationship with Margaret's family, he should have decided to include them as significant beneficiaries of his estate.

'The relationship had moved on considerably from the position in 2007.

'Jack Leonard made a wholly reasonable and understandable will in 2015. He did not cut out or exclude any of his own family, for whom he obviously had deep love.

'He did include his wife's family, whom he had come to look on as his own.. He knew who they all were - his own children and his step-children and step-grandchildren - and he treated them all equally.'

The judge is expected to give her ruling on the dispute at a later date.