An 85-year-old former Catholic priest has admitted sexually assaulting seven children, including altar boys, after spending more than 20 years on the run in Spain.

Francis Paul Cullen was extradited back to the UK last year to face the charges after being traced to Tenerife. The Catholic Church and its safeguarding board helped police to trace Cullen, who was found to have attended mass at a church in Playa de las Americas every Sunday.

On Monday Cullen, looking frail in the dock, pleaded guilty to 21 charges at Derby crown court. The offences, committed between 1957 and 1991 on children aged between six and 16, took place while Cullen was a practising priest in Mackworth, Derbyshire, and later Buxton, Derbyshire, and Hyson Green, Nottinghamshire. Cullen pleaded guilty to 15 counts of indecent assault, five of indecency with a child and one of attempted buggery.

Judge Jonathan Gosling told Cullen, who was born in Dublin, that a "very substantial" custodial sentence was inevitable.

Prosecutor Sarah Knight told the court Cullen was extradited from Tenerife last year on a European arrest warrant containing a series of charges of sexual abuse. She said further complainants had come forward and, because of the European arrest warrant, they had needed to seek the permission of the Spanish authorities to charge Cullen with further offences. But Cullen agreed to the further charges, meaning they no longer needed to seek the authorities' approval, the prosecutor told the court.

Following the guilty verdicts, the judge adjourned sentencing until 24 March. Cullen was remanded in custody.

Speaking after the verdict, Detective Constable Matt Goodwin, from Derbyshire Police, said: "I would very much like to thank the victims of this case for coming forward to the police. It is due to them that Cullen had today pleaded guilty to the offences. Without their help and support, this man would still not have been brought to justice."