1. A data processing apparatus comprising: a data processor for processing data in a secure and a non-secure mode; a memory for storing said data, said memory comprising a secure portion and a non-secure portion, said data processor in said secure mode having access to data stored in said secure portion that is not accessible to said data processor in said non-secure mode; and a further processing device for performing a task in response to a request from said data processor issued from said non-secure mode, said task comprising processing data at least some of which is secure data, said further processing device comprising a secure data store, said secure data store not being accessible to processes running on said data processor in non-secure mode; wherein prior to issuing said request, said data processor is adapted to perform a set up operation on said further processing device, said set up operation being performed by said data processor operating in said secure mode and comprising storing secure data in said secure data store on said further processing device, said secure data being secure data required by said further processing device to perform said task; wherein in response to receipt of said request from said data processor operating in said non-secure mode, said further processing device performs said task using data stored in said secure data store to access any secure data required that is stored in said secure portion of said memory, wherein said stored secure data comprises at least one address in said secure portion of said memory, said further processing device accessing secure data stored in said at least one address while performing said task.