I have worked around the issue with an SSIS package, I am aware of the Trustworthy option and the security implications which is why I opted not to use it.
I have created an SSIS Package with for loop to move the files from the UNC resource to a local resource; the xml files are then processed and deleted for those processed successfully.
By using SSIS I am able to build in a little more advanced error handling as well.
Not ideal, but I do prefer it to the Trustworthy option.
Thank you for your feedback