TWO detectives who investigated an allegation of child abuse involving disgraced rock star Ian Watkins have a case to answer for misconduct for not pursuing all reasonable lines of inquiry, the police watchdog has ruled.

An investigation by the Independent Police Complaints Commission (IPCC) found that Bedfordshire Police took immediate steps to investigate an allegation of child abuse involving the former Lostprophets frontman in 2012 and to safeguard a child.

However, the IPCC recommended that two detectives have a case to answer for misconduct for not complying with force policy on recording decision-making, and not pursuing all reasonable lines of inquiry.

Watkins was sentenced in December to 35 years in prison for a string of child sex offences including the attempted rape of a baby.

The IPCC investigation into Bedfordshire Police began in January last year after the force received a complaint from Joanne Mjadzelics, Watkins former partner, who was recently cleared of possessing indecent images.

It was concluded that neither officer has a case to answer in respect of Ms Mjadzelics's complaint that they failed to protect an 18-month-old infant, Child A.

The investigation found that Bedfordshire Police acted promptly to investigate Ms Mjadzelics's allegation that the child's mother, referred to Miss A by the IPCC, was allowing Watkins to sexually abuse her child.

IPCC commissioner Jan Williams said: "Bedfordshire Police officers did respond in a timely way to the allegation made by Joanne Mjadzelics in 2012, and demonstrably had the welfare of Miss A's child uppermost in their minds.

"Nothing was found by our investigation to say the force could definitely have prevented any offending, or contributed to bringing Ian Watkins to justice sooner.

"However, there were some more investigative steps detectives could have taken, including the earlier seizure and analysis of electronic equipment belonging to Miss A.

"The two officers subject to the IPCC investigation stated that they did not believe there were grounds to seize Miss A's devices, and it is regrettable that they failed to document their decision-making in this regard."

The IPCC found the detective constable and the supervising sergeant did not progress the investigation adequately.

Miss A was arrested on November 21 2012 as a result of inquiries by South Wales Police into Watkins's online activity.

The IPCC has agreed with Bedfordshire Police's decision that the two detectives should receive management action.

There are continuing investigations into South Wales and South Yorkshire Police over their handling of allegations against Watkins.

Miss A and another woman entered guilty pleas to a number of sexual offences.