Police today said they believe missing Sian O'Callaghan could still be alive.

Speaking outside Gablecross Police Station in Swindon, Chief Superintendent Steve Hedley said: ''A short time ago, a man was arrested on suspicion of the kidnap of Sian O'Callaghan.

''He was arrested by Wiltshire officers in Swindon. It is a significant development in this investigation.

''Our priority is to find Sian and we are doing all that we can to do that.

''This is an exceptionally busy time for us and my officers and we will update you as soon as we can.

''We hope that Sian is alive. We are working on finding her and recovering her.''

He would not confirm whether the man arrested was the driver of a green Toyota Avensis estate which was swooped on by officers at Asda Walmart in Swindon earlier yesterday morning.

He added: ''Searches in Savernake Forest are still on-going.''