Children must not be locked up overnight in police cells, a Bradford councillor has warned – after new figures revealed thousands are across the district.

Coun Ralph Berry, the Council’s executive member for education, demanded action after an investigation by the Howard League for Penal Reform.

The prison reform organisation found that 3,729 under-17s were held overnight by West Yorkshire Police in 2011, of which 3,093 were boys.

That was the second-highest figure anywhere in England and Wales, behind only the giant Metropolitan force (13,860).

The controversy will be raised at Parliament today, when the Association of Police Officers is quizzed on the practice by MPs.

And Frances Crook, the Howard League’s chief executive, said: “Holding children as young as ten in police cells overnight is unjustifiable.

“The vast majority of children who are locked up are innocent of any crime and it is a frightening and intimidating experience which does more harm than good.”

That criticism was echoed by Coun Berry, who said: “There must be a better way of providing secure accommodation for young people.

“They may have very challenging behaviour, but they are children. They need to be kept away from the adults who get locked up after what goes on in Bradford on a Saturday night.

“I wonder whether putting children in police cells overnight is a matter for the UN Convention on the Rights of the Child?

“I hope this is something that West Yorkshire Police and the crime commissioner, working together with local councils’ children’s departments, will address.”

Phil Wiggins, West Yorkshire’s chief inspector, insisted the force avoided locking up children “wherever possible”.

He pointed out that fewer were detained overnight in 2011 than in the previous year, when the total was 4.469.

However, Chief Inspector Wiggins said: “There are occasions when making an arrest is necessary both for the safety of the suspect and to ensure proper procedures are followed.

“Where appropriate, we do seek to make use of ‘out of court’ disposals, rather than putting them through the criminal justice system.”

The Home Office declined to comment on the issue, insisting whether children were detained was an operational matter for police forces.

Official guidance says cells should not be used for juveniles “unless no other secure accommodation is available” – but does not appear to mention overnight stays specifically.

The Howard League said an average of 112 under-17s were being locked up overnight every day in 2011 – a total of more than 40,000 across the country.