To do this you must ask the convict to write to you a letter along the following lines:

To whom it may concern.

I hereby give to ( name) the right to act on my behalf in all matters concerning the re-investigation of the case of my present conviction. This shall  include access to all documents presented at my trial and any other ancillary evidence lawfully granted to me. I also give permission to (name) to act on my behalf in pursuing, in a lawful manner,  a re-investigation of my case with a view to obtaining fresh evidence. I give permission for (name) to discuss my case in confidence with my solicitor; this permission does not extend to taking  any decision as to sending a petition to the Criminal Case Review Commission without my further express permission in writing.   I do not grant permission to (name) to publish, or cause to be published in any way,  any of the evidence obtained as a consequence of my granting this permission. Nor do I grant permission to (name) to benefit in any way, financially or  otherwise, from the material that may be obtained as a consequence of my granting this permission. 

Signed

Date