Parents have expressed their devastation at the sudden closure of a special needs residential school in Bristol, which left their children – who have severe and complex learning difficulties – distraught and without suitable alternative placements.

Parents were called at work and summoned to pick up their children from St Christopher’s – an independent special school and care home in Westbury Park in the north of the city – after the schools’ regulator Ofsted suspended its registration because of safeguarding concerns.

Police have confirmed they are investigating allegations of child cruelty and a number of staff have been suspended pending the outcome of the investigation. However, parents are furious at the way the closure was handled, with little warning or apparent forethought.

Parents were handed their children’s belongings in black binbags, while some children were bussed to emergency placements around the country. Other parents, who have not lived with their children for years due to their extreme, challenging behaviour, had no choice but to take them home.

One parent described witnessing an “auction”, as alternative providers selected pupils they were willing to take on while rejecting others. Some parents said they were having to give up work to look after their children; others said their children had been traumatised by the experience and had regressed.

“I feel they have left the children in a more vulnerable position than if they would have stayed there,” said James Cole, whose 13-year-old son Jacob has lived at St Christopher’s for a year and a half. “To just pull the plug without any due care to the lives of those children is unbelievable.”

Facebook Twitter Pinterest James Cole with his son, Jacob. Cole said it took months of careful investigations for parents with children like Jacob to find suitable placements. Photograph: Adrian Sherratt/The Guardian

Jacob, who has autism, epilepsy and displays challenging behaviour, is now at home while his parents struggle to find an alternative place. “St Christopher’s was quite unique in that it took so many children with so many complexities because they had such good services there. It’s hard to find that replicated elsewhere.”

Cole said it took months of careful investigations for parents with children like Jacob to find suitable placements, which can cost around £300,000 a year. Yet the sudden closure of St Christopher’s meant some children were moved elsewhere in hours. “It was absolutely dreadful,” he said.

One mother, who asked to remain anonymous, described seeing her 15-year-old son lying on the grass sobbing, his carers lying alongside, cuddling him and crying too. “These poor children. It’s had a massive impact on them,” she said.

“It’s heartbreaking, absolutely heartbreaking. Parents were standing with their children’s belongings in black bin bags, crying, while their children were being loaded into vans and being sent to other areas of the country. I understand they had their reasons [for closing the school], they are protecting our children, but they’ve made these children very vulnerable.”

Her son is now at home, which will have an enormous impact on family life. “He is very stressed. He is going to miss all the really good carers who looked after him. He had an amazing team around him. We will not let our son go anywhere else now.”

Other parents are having to contemplate travelling huge distances to find a suitable placement. “We live in Bath and we’ve been offered a place in Northumberland or Shrewsbury,” said Kevin Maxwell, whose 16-year-old son, Jonah, is one of the 27 pupils moved out of St Christopher’s last week.

An Ofsted spokesperson said St Christopher’s was inspected in June and judged to be inadequate. The inspection related to the residential part of the provision, rather than the school. “On Monday 29 July, we issued St Christopher’s with a suspension of registration notice because of serious concerns about safeguarding.”

Avon and Somerset police confirmed: “We’re investigating allegations of child cruelty offences relating to a special education school in the north Bristol area. We’re working with our multi-agency partners to ensure that safeguarding measures are being put in place and Ofsted has been notified. Parents have been contacted. Some members of staff have been suspended while our investigation continues.”

In 2016 St Christopher’s was threatened with closure because it had become economically unviable and was taken over by the Aurora Group, a private company specialising in special education care. An Aurora spokeswoman said: “We are deeply concerned about the serious allegations against a small number of staff who were immediately suspended,” a spokesperson said.

“They were reported to the authorities straight away in line with our safeguarding procedures. We are now focused on doing all that we can to support the children, young people, their families and carers, and the many caring and dedicated staff who are affected during this difficult time.”

Dr Jacqui Jensen, executive director of people services at Bristol city council, which is one of the local authorities responsible for pupils at the schools, said: “We are working with the families, other local authorities and a range of partners to review everyone’s individual care plans and make alternative arrangements for the provision of care and education.”