Ritalin prescription

How might we actually obtain a Ritalin prescription quickly in a situation where the prescribing psychiatrist has sent details to the GP to issue the actual prescription, but the GP has then refused to prescribe it on the basis that this is the "local area policy"?  Going back to the psychiatrist has simply generated 2 slow options of 1) changing GP or 2) them writing to the CCG for permission to prescribe directly.  Neither of these options seem likely to help soon enough when important exams (for which focus and concentration are needed) are coming up in a couple of weeks time.

It's for an autistic adult with strong features (but not a diagnosis) of ADHD.

Any ideas?