In his mind’s eye, Ian Simpson can picture his grandchildren playing happily in the garden of his thatched cottage in rural Suffolk.

It is what keeps the former IT consultant focused. By rights, Mr Simpson, 69, should be enjoying retirement in the quintessentially English village of Hartest where he keeps fit cycling along centuries-old lanes.

Instead, along with his ex-wife Linda, he is engaged in a desperate international custody battle for Jack, seven, and five-year-old Alice, who are pawns in an extraordinary saga of jealousy, blackmail and vengeful murder and live 6,000 miles away in a cramped flat in a central China backwater.

The facts of the case are undisputed. A year ago their father Michael Simpson, 34, the head of Next’s retail operations in China, was confronted by his estranged wife Fu Weiwei, the children’s mother, at his apartment in Shanghai. In a jealous rage, Weiwei took a knife from her handbag and flew at his new partner, Rachel Lin, slashing her arms ‘to the bone’.

Then, as Michael cradled Rachel in his arms, screaming for an ambulance, Weiwei plunged the blade into both sides of his neck, killing him instantly.

Next Fashion boss Michael Simpson was stabbed to death by his vengeful Chinese wife Fu Weiwei a year ago (pictured together on their wedding day)

Jack and Alice, who had enjoyed a privileged life in Shanghai, were taken 600 miles away to live with their impoverished maternal grandparents.

Incredibly, they still have no idea that their father is dead or that their mother is facing a long prison sentence. They believe they are working abroad.

Now, in a disturbing new development, The Mail on Sunday can reveal that Weiwei’s parents are finally willing to grant Mr Simpson and Linda custody of their grandchildren – but only if they pay £62,000.

‘It is an outrageous attempt to use the children as pawns to extort money from us,’ Mr Simpson said. ‘Our lawyers said the demand was very near to being an illegal act of selling children.

‘We just want what is best for our grandchildren. They will have a better upbringing here in the UK. It is wrong that Weiwei’s family should attempt to make us pay.

‘We have already lost our son due to her and we do not want to lose our grandchildren as well.’

Navigating the confusing Chinese judicial system, the Simpsons have behaved honourably at all times, even under provocation, which is why they find the demand for money such an indignity.

Last month Weiwei’s family agreed to let Mr Simpson and his ex-wife visit the children for the first time in nearly a year.

They met for six hours in a hotel in the industrial city of Xiangyang. Mr Simpson said it was ‘fantastic but very emotional’, adding: ‘Michael and Weiwei were not even mentioned. It just seemed ludicrous that the children did not know – but we could not tell them and then just walk away.

‘Jack was very quiet and only said the odd word. I tried to read to him from Wind In The Willows and he was struggling to understand as he had not spoken English for a year.

‘He cried when we showed him pictures of his father. He just sat on my lap for 40 minutes and never left my side. At the end, he said, “Can I stay here with you?” and I had to say, “No, you have to go”.’

Michael Simpson travelled to Shanghai in 2009 to work as a senior manager for Next as it expanded its operations in the Far East. He met and married Weiwei, a shop assistant, soon after arriving. The couple separated in 2015 and Mr Simpson became romantically involved with Ms Lin, who went to university in Britain.

His father, Ian Simpson, is locked in a legal battle to have their children, Jack, seven, and five-year-old Alice, brought to England (pictured together earlier this year). They are currently living with their maternal grandparents

Weiwei, who admitted murder, faces a possible 25-year prison sentence. This is likely to be reduced as the Simpsons are prepared to offer ‘forgiveness’ – a feature of Chinese law enabling an offender to receive a reduced sentence.

As a further concession, Mr Simpson and Linda said they would waive their right to compensation from Weiwei’s family for the murder. In return, Mr Simpson said they were promised the children.

But then came the final insult.

Mr Simpson was told the cynical demand for money was actually a ‘deposit’ to pay for flights and travel costs for the children to return to China at least once a year.

After Michael and Weiwei separated, Jack and Alice lived with their father in his spacious Shanghai apartment. Explaining the background to the break-up, Mr Simpson said: ‘She was a lot younger than him and wanted to go out and spend money and go to clubs.

‘Weiwei was quite lazy and would spend all her time looking at her phone when she and Michael came to the UK to visit us.

‘She was aged 25, but going on 16.’

Mr Simpson said problems developed in the couple’s marriage soon after Alice was born.

‘She last came over here with him about five years ago. She was miserable and hardly talked. Michael had a cut on his head. It was because she had thrown a plate at him. I said he should really divorce her. He said, “The trouble is that she is violent”.’

Weiwei eventually left Michael and the children when Alice was two. Shortly before he was killed, Michael began a new relationship with Ms Lin. Mr Simpson said: ‘He told me at Christmas in 2016 that he was getting close to Rachel and then he said they were moving in together in January last year.

The children have no idea their father is dead or that their mother is facing 25 years in prison. Their grandparents want them to return to Britain because they believe they will be better off in Britain

‘We were told that Weiwei had the children for a weekend and brought them back on the Monday morning when she saw a bag which was obviously Rachel’s. She went home and came back at 8pm that evening with two girlfriends to confront Rachel.

‘I think she wanted to take a photograph of her to put on social media in an attempt to shame her.

‘The three of them started yelling at Michael. Rachel came out of the kitchen, and the two friends yelled, “There she is”. Weiwei then rushed at her, took a knife from her bag and stabbed her in the shoulder and arm, cutting through an artery so blood was spurting out. They were deep and horrific cuts. Michael went to pick her up and screamed for an ambulance. He was holding Rachel with his back to Weiwei when she stabbed him on both sides of his neck and he died instantly.’

The children slept through the murder and were woken by police, who took them out of the flat without saying what had happened.

Mr Simpson said he heard of his son’s death after Ms Lin left a voicemail message on his former wife’s phone. ‘It was so confusing,’ he said. ‘It was weird because there was a lot of noise and it sounded like Michael’s voice in the background. I was hoping that it was some sort of mistake. I was thinking that maybe they were drunk, and it was a practical joke.

‘Then five hours later my other son Andrew called to say that Rachel had called again from hospital and confirmed it. I was devastated. The next day, I was nearing the gate for the plane to Shanghai, but when I saw it, I suddenly sat down and cried – I didn’t want to get on knowing what was at the end of the flight.

‘On the plane I tried watching an action movie to distract me. As it finished I could feel the pain welling up and I had to go to the toilet where I just screamed. Luckily it was drowned out by the engines.

‘Michael had a spark about him. He was always amazing with kids. If he walked into a room with children around, they would be all over him within minutes. I would hear the football results every Saturday, and a minute later I would get a text from Michael in China, talking about it. Now I look at my phone and there is no text. It is silly things like that.’

Mr Simpson said his family had sent cards, gifts and books to Jack and Alice since Michael’s murder, but they had not been passed on to them.

‘We had a picture book made up with photographs of Michael and we sent that to them but we found out that they had not seen it. When we saw the parents, we realised nothing had been passed over.

‘It is her brother who has been pulling the strings. The brother told us in November that he had told the children that we didn’t love them and didn’t want them.

‘The only thing we received from China was a couple of pictures of the children at school.’

Mr Simpson said he believed his grandchildren would have a better life being brought up by their relatives in the UK.

He added: ‘Their Chinese grandparents are fairly uneducated. The grandfather cannot read or write, and the grandmother can only read a little. I don’t think they are being mistreated, but how do they read to the children?

‘They will be better off over here, having their own bedrooms and all the comforts of home. They will have a whole network of relatives here and we have places waiting for them at school. All our other grandchildren do things like ballet and Scouts, but there is nothing like that over there. Everything from schooling to play areas and other facilities are better here.

‘We have even lined up a Chinese tutor for them so they can keep their Chinese up. We want their family in China to stay in touch. If they stay in China, they will become more and more Chinese, and we will have lost them.’

Mr Simpson’s existence is as far removed from his grandchildren’s life in the town of Nanzhang as is possible to imagine.

Most people, including Jack and Alice, live in crumbling low-rise apartment blocks and the ramshackle town centre is packed with vegetable and fruit sellers who bring their produce in from the countryside on bicycles and motorised rickshaws.

Foreigners are hardly ever seen and locals stop in their tracks and stare at the sight of any Westerner.

Alice, who went to an exclusive international school in Shanghai, now attends a government school on the dusty outskirts of the town where she is the only foreign pupil.

For now, the custody case remains deadlocked. Mr Simpson said his lawyers had officially rejected the demand for money, and they are set to launch a civil battle for custody, but this can’t begin until after Weiwei is sentenced.

A friend has set up a crowdfunding website to help cover legal costs.

Mr Simpson said: ‘Bringing up the children here will be a hard slog, and people say, “Do you really need to be looking after children at your age?” But there is no alternative.

‘Losing Michael has put a hole in our souls and if we lost his children as well, then that hole would be ten times bigger and we would have lost his whole family.’