An engineering firm has pleaded guilty to health and safety breaches after the death of a seven-year-old boy whose body was found wedged in a pipe on a building site.

Conley Thompson went missing on July 26 2015 after telling his mother he was going out to play with friends in Barnsley, South Yorkshire.

A search was launched and his body was found the next day in a pipe on the building site in Worsbrough.

On Tuesday, Howard Civil Engineering, which was responsible for the site, admitted two health and safety breaches.

Managing director Michael Howard pleaded guilty on behalf of the Leeds company to breaching regulation 13(4)(b) of the Construction (Design and Management) Regulations 2015 and Section 3 (1) of the Health & Safety at Work etc Act 1974.

The company failed “to ensure necessary steps were taken to prevent access to the site by unauthorised persons”.

Andrew McGee, prosecuting on behalf of the Health and Safety Executive, said fencing around the site, which was “slap bang in the middle of a residential area”, was “significantly substandard”.

He told Barnsley Magistrates’ Court: “Either (the fencing) wasn’t a suitable height or it was non-existent, or, where it did exist, it was poorly maintained.”

Mr McGee said industry guidance notes “many children see construction sites as adventure playgrounds” and they should be protected against the dangers “even though they may be entering as trespassers”.

Pictures shown to the court included one of a police officer standing next to perimeter fencing that was “nowhere near six-foot high”, and another of a health and safety inspector with the fence “barely … up to his chest”.

Mr McGee said there was “clear evidence that both adults and children were frequently and easily gaining access to the site”.

He told the court one Howard Civil Engineering worker “was aware people had been climbing over the fence, getting in”, while another remembered “kids” trying to get on to the site but being chased away.

A child previously said Conley had been seen on the cages containing the black pipes and was “running across the top of the cages”, Mr McGee said.

The boy “clearly had a history of going on to the Church View site” and it was “a location he found tempting to enter”, the court heard.

Mr McGee said: “He was not alone in this amongst the children of this residential area.”

He added: “There is no precise timeline for the events of that day. Despite intensive investigations, there is no evidence of when, how, or, if he was not alone, with whom Conley entered the site prior to his death.”

Mr McGee said a pathologist concluded Conley must have gone into the pipe, designed to house fence posts, with both feet at the same time.

“The pathologist says it’s possible he slipped in with both feet while standing on the edge, or he might have lowered himself in – nobody knows,” he said.

There was no suggestion of foul play, the court heard.

Mr McGee said: “The company fell far short of the appropriate standard. It failed to have in place perimeter fencing consistent with industry standards.

“Perimeter barriers were obviously, we say, inadequate and, in some places, non-existent.”

James Maxwell-Scott, mitigating, said managers at the firm were not aware children had been on the site before the fatal incident.

He said: “Conley Thompson’s death was a tragedy for his family and friends.

“The defendant hopes the conclusion of this prosecution will help in some small way to bring an element of closure.”

District Judge Naomi Redhouse adjourned the case to Sheffield Crown Court for sentencing.

At the time of his death, Conley’s grandmother Deborah Fraser said she was “shell-shocked”.

She said: “As a person, he was a lovely little lad, boisterous, got into anything and everything but his smile could light up a room.”