The mother of the missing university chef Claudia Lawrence has said “if you give up on hope, you may as well give up altogether” as she marked the 13th anniversary of her daughter’s disappearance. Lawrence, 35, has not been seen since she failed to turn up for work at the University of York in March 2009. Detectives believe she was murdered, but no body has been found despite numerous appeals, arrests and searches. In an interview to mark the 13th anniversary of Lawrence’s disappearance, her mother, Joan Lawrence, said she had been given “hope so many times and it’s been dashed”. She told BBC Radio York on Friday: “I can’t believe it’s 13 years. I shouldn’t be. We should really have had answers before now.” Police work on the case increased last year when the North Yorkshire force spent two weeks searching a lake and nearby woods just outside York. Officers later said that “nothing of obvious significance” was found. Lawrence’s mother said: “I have had hope so many times and it’s been dashed. I never give up on hope. If you give up on hope, you might as well give up altogether. “It’s the not knowing. Despite the fact she was 35, she is my child. You can’t say goodbye, you don’t know whether she’s dead, you don’t know if she’s alive, you don’t know where she is, you don’t know what’s happened to her, there’s no grave … It’s still pretty awful, it really is.” Lawrence’s father, Peter, died last year without knowing what happened to his daughter. He had campaigned to get answers to the puzzle of her disappearance and spent years arguing for what became the Guardianship (Missing Persons) Act – also known as Claudia’s law – which allows relatives to take control of their missing loved ones’ financial matters. Joan Lawrence said she would continue to try to solve the mystery herself and was reviewing the details “with a fine-toothed comb” for “simple things that have been missed”. North Yorkshire police have conducted two investigations and questioned nine people in relation to her disappearance – and suspected murder – but no charges have ever been brought. Speaking after he took over as the senior investigating officer on the case last year, Det Supt Wayne Fox repeated the belief that several people know, or have suspicions about, what happened to Lawrence.