It is now thought the target might have been the boy’s mother.

The couple had initially settled in Wolverhampton after fleeing war-torn Afghanistan 11 years ago.

Last year she left her husband, a taxi driver, and moved to a house in Worcester with their three children, now aged ten, eight and three, to start a new life.

A neighbour recalled shouting matches between the couple, while another said when the woman left her husband broke down in tears claiming she would not let him see their children.

It is believed the thugs who carried out the acid attack on the boy had been monitoring the family after tracking them down to their new semi-detached home.

Detectives have been questioning residents about sightings of suspicious people and vehicles in the area.

When the pair were in a relationship she would wear a full veil but in recent years had removed it and moved to an address in Worcester 30 miles away with the children.

It is believed the estranged father discovered the whereabouts of his wife when a photo appeared in a local newspaper showing one of the children at a local event.

It is alleged that the gang bungled the attack and the three-year-old got splashed with the noxious substance accidentally in the process.

Police have now arrested four men - but none of them in Worcester. Three were in Walthamstow, London, last night and another in Wolverhampton

Police have now arrested four men – but none of them in Worcester. Three were in Walthamstow, London, last night and another in Wolverhampton

A West Mercia Police source confirmed to MailOnline that the older detainee is the victim’s father from Wolverhampton.

She said today: ‘He is still in custody. No charges as yet have been brought. This is an ongoing investigation.’

The man, who is understood to have split up from his partner and mother of his toddler son, is being held on suspicion of conspiracy to commit grievous bodily harm.

The mother had been hiding in a safe-house after a fractious break up.

Following the attack she and her son, who was treated in hospital for acid burns to his hands and face, were moved into a police safe house amid fears they could be attacked again.

Mark Travis, Chief Superintendent of West Mercia Police, hinted that a community dispute may have led to the vile attack

Mark Travis, Chief Superintendent of West Mercia Police, hinted that a community dispute may have led to the vile attack

She had been living with the toddler and her two other children in a secluded residential street in Worcester after fleeing the family home in Wolverhampton because of ‘difficulties within her relationship,’ a new neighbour said.

Her child suffered serious burns when a bright pink acid was thrown over him as he sat in his pushchair in the city’s Home Bargains store on Saturday while his mother shopped.

Four men have been arrested in connection with the attack – and she is now in a safe house with her son under police protection amid fears they could be attacked again.

One neighbour said there had been ‘bad blood’ caused by a family dispute and said the attack may have been launched over the end of a relationship with the three-year-old’s mother, who could have been the true target.

A source close to the investigation revealed the mother, who has not been named, had fled to Worcester from Wolverhampton after ‘difficulties within her family’.

A 39-year-old was later arrested in the city.

The source said: ‘She had moved to Worcester from elsewhere but hasn’t been here long. She had moved because of difficulties within her family.

‘Nobody knows her really well and she didn’t have any connection with Worcester. That’s why she was moved here, because she was fleeing her previous situation.

‘Somehow the parties she was in a dispute with found out where she had moved to and that’s how this horrendous incident has happened.

‘The acid attack was targeted at her. The child just happened to get in the way.’

Chief Superintendent Mark Travis, who is leading the investigation, says he is keeping an ‘open mind’ about the motive and target of the attack.

But hinting about a row he said: ‘This is not the way to resolve issues and disputes in communities’.

Chief Superintendent Mark Travis said: 'At this time we are treating this as a deliberate attack on a three-year-old boy.' Pictured: The men wish to speak to

Chief Superintendent Mark Travis said: ‘At this time we are treating this as a deliberate attack on a three-year-old boy.’ Pictured: The men wish to speak to