Officers are looking for any sign of the 24-year-old student from Kent last seen in the German city of Aachen on 30 July 2001.

Miss Kerton was returning to the UK after visiting her fiancé's mother, Ramana Simon, at the family's home in the village of Strassfeld near Bonn.

Nearly 200 officers have begun a fourth day of combing through fields and a quarry near Strassfeld.

'Quarry search'

Miss Kerton's family believe she is dead and have criticised German police over what they believe has been a lack of positive action.

A police spokesman said: "The police are still searching today but have so far found nothing.

Ms Kerton had been visiting her fiancé's family

"They are still concentrating on land and the quarry.

"We still do not know how long the search will take."

He said it may carry on into Friday.

On Wednesday, Miss Kerton's father, Phil, originally from Abergavenny, in Wales, said the family had been "dismayed" not to be officially told about the search.

He believes his daughter was murdered but the German authorities only recently began treating the case as a criminal investigation.

Miss Kerton, from Broadstairs, was last seen when she was dropped of at Aachen station by fiancé Peter Simon's mother.

Criminal investigation

Her disappearance came days after she failed her final nursing exams.

At the time her father said his daughter was depressed about failing her exams and felt the death of her schoolfriend Lucie Blackman had affected her performance in her finals.

In June this year German prosecutors agreed to launch a criminal investigation into Miss Kerton's disappearance in a move welcomed by her parents.

Mr Kerton had earlier hired formal royal protection chief Dai Davies to investigate his daughter's disappearance and criticised the German investigation.

The couple have spent their life savings looking for their daughter and relatives from all over Wales have joined searches in Belgium and Germany.