A council care worker who repeatedly raped one girl and abused three others has had his jail sentence increased to ten years.

Gordon Collins was originally sentenced for six years after committing indecency offences against four underage girls in two Edinburgh children's units and repeatedly raping one of them.

The Crown successfully appealed against the sentence imposed by the trial judge, Lady Wise, arguing it was "unduly lenient".

Lord Brodie told the rapist via a video link to Barlinnie prison in Glasgow: "As the trial judge observed in her sentencing remarks, Collins committed an appalling series of offences involving the predatory sexual abuse of four vulnerable teenage girls.

"He was in a position of trust in relation to each complainer and the offences comprised a gross breach of trust.

"Although he had no analogous convictions, he has shown no remorse and continues to deny responsibility for the offences."

Lord Brodie, who heard the appeal with Lady Clark of Calton and Lord Turnbull, said: "The court is bound to hold that the sentence of six years falls outside the range of sentences reasonably open to the trial judge and is unduly lenient.

"A sentence of ten years' imprisonment would, in our opinion, be appropriate."

The appeal judges quashed the original sentence imposed on Collins and substituted the higher prison term on the sex offender.

Collins, 60, was a residential care worker at Northfield Young Persons Unit and St Katherine's Secure Unit, both in Edinburgh, when he committed the abuse between 1995 and 2006.

Lord Brodie said: "Each of the four victims was in some way troubled or had experienced a difficult upbringing."

"The evidence disclosed that over a period of some 11 years he groomed each of the victims, gaining their trust and making them feel special before sexually abusing them," said the senior appeal judge.

Advocate depute Iain McSporran QC told judges at the Court of Criminal Appeal in Edinburgh that the jail term was "far below" what it ought to have been for punishment and deterrence.

He maintained "a significantly more substantial custodial sentence was required".

Mr McSporran said: "The contention of the lord advocate is the sentence, in all the circumstances, does not adequately reflect the gravity of the charges."

The judges were told victims were vulnerable young people, often from troubled backgrounds, who were entitled to expect sanctuary.

Lord Turnbull said during the hearing: "Many of these children are removed precisely to provide protection."

Collins, formerly of Wolsey Avenue, Bonnyrigg, Midlothian, had singled out victims for treats, outings and attention before exploiting them.