Taxi driver Christopher Halliwell, who has admitted murdering nightclubber Sian O'Callaghan, has escaped justice over a second murder because of a police blunder, it can be reported today for the first time.

Halliwell, 48, pleaded guilty to killing Miss O'Callaghan during a hearing at Bristol Crown Court.

Halliwell, of Ashbury Avenue, Swindon, was also accused of murdering Becky Godden-Edwards but that charge was withdrawn following a ruling by a High Court judge - even though he led police to her body.

Mrs Justice Cox ruled that the confessions the father-of-three made to killing both women during a three-hour period on the day of his arrest were inadmissible because Detective Superintendent Steve Fulcher breached police guidelines governing the interviewing of suspects.

The detective, who was leading the hunt for Miss O'Callaghan, failed to caution Halliwell and denied him a solicitor.

Police have vowed to get justice for Miss Godden-Edwards and revealed that Mr Fulcher has been suspended pending an investigation by the Independent Police Complaints Commission (IPCC) into allegations of "inappropriate contact with the media".

Miss O'Callaghan, 22, disappeared after leaving Swindon's Suju nightclub in the early hours of March 19 last year after a night out with friends. Hundreds of volunteers turned out at Savernake Forest to help in the search for her but police found her body in Uffington, Oxfordshire, on March 24 after being taken there by Halliwell.

Miss Godden-Edwards's remains were discovered at a Cotswold beauty spot after Halliwell was detained by detectives investigating the disappearance of Miss O'Callaghan.

Office worker Miss Godden-Edwards, who would have celebrated her 30th birthday earlier this year, was last seen by her family in Swindon more than eight years ago. On the night she disappeared, Halliwell had signed off from work but instead of going home he cruised the streets of Swindon in his green Toyota Avensis taxi looking for a victim.

Miss O'Callaghan left the nightclub at 2.53am for the short walk to the home she shared with boyfriend Kevin Reape. Shortly after she walked past the Goddard Arms on the High Street in the Old Town area, she fell into Halliwell's clutches by getting into his taxi.