If your partner already has a CPAP machine and is still showing 14 AHIs per hour, he MUST go back to the sleep clinic because that level of AHIs shows that he is not being effectively treated for his condition. The appropriate level is under 5 per hour, and I'm not surprised he's still feeling tired - and possibly not working as efficiently as he might with adequate deep sleep.
It's important that the pressure is correct for his requirements ... and that his mask fits comfortably. These can both be checked easily at a sleep centre.
However, it IS difficult to settle to the idea of using a CPAP machine, and this will take perseverence and lots of encouragement. We can help with the latter as can you!
Don't let his work get to his records before he sees his doc, and even afterwards if at all possible. Sleep apnoea is covered under the DDA, and so he should be protected if his employer has a gripe. I can't help a lot with this because I no longer live in the UK, but there are members here who have expertise in this area. I hope they'll get in touch soon.
If possible, push the doc to see him earlier if there's any possibility of a cancellation appointment.
Just to remind you - his medical records are CONFIDENTIAL and he and his doc should discuss exactly what disclosure should be made IF ANY.
I hope the situation improves soon for both him and you. Thank you for your courage in posting and please let us know how things go.