There is insufficient evidence for a manslaughter prosecution relating to the deaths of three men and a teenage boy who were killed in an explosion at a water recycling centre, police have said.

Luke Wheaton, 16, from Bradley Stoke, Ray White, 57, from Portishead, Brian Vickery, 63, from Clevedon, and Mike James, 64, from Bath, died in the incident at the Wessex Water site on December 3 2020.

It is understood that Mr James was a contractor working at the site, while Mr Vickery and Mr White were employees of Wessex Water and Luke was an apprentice at the firm.

In a statement issued on Wednesday, Avon and Somerset Police said its major crime investigation team had been leading the inquiry into the cause of the explosion, assisted by the Health and Safety Executive (HSE).

A force spokesman said the investigation had focused on whether any individuals were responsible for the explosions, as well as whether any health and safety offences had been committed.

Detectives, along with HSE investigators, recently met with the Crown Prosecution Service to review the case and it was decided there was “insufficient evidence to provide a realistic prospect of a criminal conviction for manslaughter”.

The HSE will now work to establish whether criminal offences may have been committed under the Health and Safety at Work etc Act 1974, the spokesman added.

Detective Chief Inspector Mark Almond, of Avon and Somerset Police, said: “Throughout our inquiry the families of Luke, Ray, Brian and Mike have been firmly in our thoughts.

“The families have demonstrated great dignity and patience while we carried out our inquiries and I’d like to publicly thank them for their support and understanding over the past three and a half years.

“Inquiries of this kind are extremely complex and require the support of other agencies to gather evidence and then a variety of experts to help us interpret what that evidence tells us.

“In this case, the evidence we’ve gathered doesn’t reach the extremely high threshold to prosecute any criminal offence of manslaughter.

“We have met all the families to explain this development and to inform them of what will happen next, with HSE taking ownership of the investigation.”

Emergency services were called to reports of a large explosion involving one of the chemical tanks at the site at around 11.20am on December 3, 2020.

The blast happened in a silo that held treated biosolids.

In tributes released through police following the tragedy, Luke was described as “the most gorgeous, loving, happy, talented, perfect son”.

Mr White’s family said he was “a wonderful son, brother and father to his two sons”, while Mr Vickery’s family paid tribute to his “cheeky and wicked sense of humour”.

Mr James’s family described him as a “brother, husband, father and Grampy”, adding that he would be missed.

Simon Chilcott, principal inspector at HSE, confirmed that investigators were in regular contact with the families of those who died.

He said: “We have been a part of this complex inquiry from the outset. Now as the lead agency, we will continue to carry out a robust criminal investigation to establish if there have been any breaches of health and safety law.”

A Wessex Water spokesperson said: “We’re continuing to work with the Health and Safety Executive as they carry out their investigations and are committed to understanding why the incident happened.

“The four colleagues will always be in the thoughts of everyone connected to Wessex Water.”