Both Claudia's mother and sister were stunned by last week's development at Sand Hutton gravel pits, near York. But as the search of the fishing lakes enters its sixth day, neither knows the reason for the new police operation.

       Claudia, 35, was last seen alive after finishing her shift in the canteen at the University of York on March 18, 2009.

       Weeks later officers said they believed she had been murdered but nothing came of the costliest investigation in the history of North Yorkshire Police.

       Last week, Claudia's mother Joan Lawrence, 77, spoke of her "utter shock" at the lakes search. She admitted she was not aware what had prompted the latest twist, adding "There must be something. Something has triggered it."

       Claudia's older sister Ali Sims, 49, was understood to be on holiday and "in the dark" about the operation.

       Last night a source close to the family said: "Joan and Ali have spoken but neither knows what prompted all this. They understand detectives may be keeping information back for operational reasons but they are desperate. Not knowing can be as hard as knowing the truth."

       Teams are currently searching woods and lakes at the beauty spot eight miles from Claudia's house.

       Det Supt Wayne Fox, who is leading the probe, said that "new information" had come to light.