Three police forces are under investigation by the police watchdog over the way they handled child abuse allegations against disgraced Lostprophets singer Ian Watkins.

The Independent Police Complaints Commission (IPCC) said it would look into how South Wales, South Yorkshire and Bedfordshire forces dealt with complaints about Watkins going as far back as 2008.

One areas of inquiry will be to explore whether Watkins' celebrity status affected the approach of detectives.

Watkins, 36, of Pontypridd, is due to be sentenced at Cardiff Crown Court after he pleaded guilty to 13 child sex offences, including the attempted rape of a baby.

IPCC commissioner Jan Williams said: "No-one can fail to be shocked by the vile details of Ian Watkins offending that emerged in court.

"As the criminal proceedings have now ended, questions are now rightly being asked as to whether Ian Watkins could have been brought to justice sooner, what steps were taken by police in response to allegations made against him as far back as 2008 and whether his celebrity status had any impact on the investigation.

"That is exactly what the IPCC is seeking to establish."

The IPCC added that it had been in contact with three other forces – Metropolitan, Essex and West Yorkshire – but they were not under investigation.

The watchdog said it began its inquiry into whether South Wales Police failed to take appropriate and timely actions against Watkins in January.

It said it would consider reports made to the force by members of the public, Crimestoppers or other police forces prior to Watkins' arrest in late 2012. It added that a number of these complaints were made by the same person.

The IPCC said one of the most significant parts of the investigation involved one officer, a detective sergeant, who was also being investigated in a separate case over claims that he had failed to act on an allegation that a 15-year-old girl had been raped.

The officer has been served with gross misconduct notice advising him that his conduct was subject to investigation.

The IPCC will also be looking into whether the separate forces could have collaborated on information regarding Watkins.

"This is complex and will take time," said Williams. "There are clearly links between the three investigations which cover a four-year period and involve numerous allegations and reports and the police response to each must be considered.

"South Wales Police are continuing to appeal for any other witnesses or potential victims to contact them. It is possible that new information may come to light which the IPCC would need to consider."

A former girlfriend of Watkins, Joanna Majic, 38, said she first warned police about his behaviour in 2008 but her claims were not fully investigated. She feared that Watkins may have abused "hundreds" of young children down the years but was being protected by their mothers.