London ( CNN ) -- A former personal assistant to Nigella Lawson told a court Friday that the celebrity chef had lied in her testimony as a prosecution witness . Elisabetta Grillo , who is accused alongside her sister Francesca of embezzling hundreds of thousands of pounds from Lawson and her ex-husband , Charles Saatchi , insisted under cross-examination she had told the truth in her own defense . Both sisters deny fraud . On Thursday , Elisabetta Grillo testified that over the years she had worked for the family , she had seen signs of cocaine use by Lawson `` every three days , I do n't know , regularly . '' In her testimony last week , Lawson confirmed she had taken cocaine half a dozen times and used cannabis in the past . But she denied being a habitual user , saying , `` I did not have a drug problem , I had a life problem . '' Asked by the prosecution Friday if she thought Lawson had lied , Grillo replied , `` Yes . '' She gave the same response when asked if Saatchi had lied . Saatchi had said in an e-mail that Lawson had used drugs regularly , but in his testimony before the court he backed off that claim . In the e-mail , which the defense shared with the court in a pretrial hearing , Saatchi wrote that the two assistants would probably `` get off '' because Lawson was using cocaine and marijuana on a daily basis and `` allowed the sisters to spend whatever they liked . '' Grillo said she had never seen Lawson take drugs but said she was aware that she used cocaine and cannabis . She recounted finding a packet containing white powder in the bathroom , rolled up bank notes , and credit cards and CDs with traces of white powder on them . Asked by her defense attorney how she felt about saying Lawson took drugs , Grillo said she did n't like it . But she said it was true . Nigella Lawson : Flirtatious celebrity chef . Personal spending . The two sisters are accused of spending large sums on luxury goods on company credit cards they were supposed to use for household expenses . Questioned by the prosecution Friday , Elisabetta Grillo insisted that Lawson had authorized spending on personal items , such as clothes , designer shoes and cosmetics , on her work credit card . She also said she 'd been told she could take out cash on the card . Grillo described Lawson and Saatchi as generous , saying the latter had paid for her to go to Paris in 2008 for her birthday . The trial has been closely followed by the UK media because of its high-profile witnesses , Lawson and Saatchi , a millionaire art collector . Allegations of drug use by Lawson emerged in June , around the time she and Saatchi were photographed having an argument in a restaurant . In the photos , which were splashed across the front pages of national newspapers , Saatchi is seen with his hand around Lawson 's throat and appears to pinch and look up her nose . Saatchi accepted a police caution for assault , and the couple announced they would divorce soon afterward . Lawson , widely known in Britain for her cookbooks and TV shows , has also appeared as a judge on ABC 's `` The Taste '' in the United States . The trial continues next week . Opinion : The rich and famous are not immune to domestic abuse .
Elisabetta Grillo insists she is telling the truth , tells court Nigella Lawson lied . The ex-aide says she was allowed to make personal purchases on her work card . Score: 6