A complaint that a member of North Wales Police staff made a racist remark to a man has been upheld by a watchdog.
The Independent Police Complaints Commission (IPCC) also said the man's claims he was the victim of a racially aggravated assault were ignored.
The force said it "regretted" the handling of the incident.
The man, 41, from Birmingham later had charges for affray and possessing an offensive weapon at a holiday park in Prestatyn, Denbighshire, dropped.
His complaint was instigated after he was arrested and taken into custody in September 2005. He was later released on bail and returned home with his family.
Once back in Birmingham, the man went to hospital and was found to have suffered a broken jaw, a fractured leg, and had to have four stitches to facial injuries.
He went to West Midlands Police and complained that he had been the victim of a racially aggravated assault by the holiday camp's security staff and that North Wales Police had failed to investigate the matter.
An investigation by the IPCC upheld two of the man's four complaints against North Wales Police.
An IPCC spokesperson said the complainant, who is Afro-Caribbean, had taken offence after a civilian staff member who was interviewing him, said his name would have originated from slave plantations.
The watchdog upheld the complaint that the comments had been racist and the staff member had since left the force.
It also made a number of recommendations to improve the force's procedures of investigating counter-claims, which it said had been "very poor".
"These were very serious allegations and included the charge that the force did not properly investigate the alleged racially aggravated assault by holiday camp security staff," said IPCC Commissioner for Wales Tom Davies.
"Our investigation found that North Wales Police procedures for dealing with counter-allegations of criminal behaviour were very poor. The force training for officers in dealing with allegations of this sort, exhibit handling and case preparation was also inadequate."
North Wales Police said it has worked with the IPCC to ensure all future allegations are thoroughly investigated and that the lessons learnt are implemented.
"Advice from the Crown Prosecution Department has been built into police procedures which will better equip investigating officers to deal with counter allegations made by those under arrest," it said in a statement.
"The racist remark made by a member of police staff was unacceptable and North Wales Police agreed with the recommendation made by the IPCC and he was to be dealt with by advice and a personal development plan, the staff member has left the force prior to this happening."
It added: "All officers and staff have comprehensive training in respect of diversity."
Following the North Wales Police criminal investigation the complainant was charged with affray and possession of an offensive weapon.
But the charges were dropped when they came to trial at Mold Crown Court in July 2006.