My experience in dealing with PHI insurers is similar to Liam's. Generally speaking, they are looking for 'win-win' solutions.
Provided there is no obvious conflict between the requirements of the course you intend doing and your inability to continue doing your former job, it is very likely that the insurers will be more than happy to facilitate your studies. Indeed, there is a possibility they may regard the course as rehabilitation and may even be prepared to part fund it, if it will allow them to cease paying the claim earlier than would otherwise have been the case.
You should ask whoever deals with your employer's income continuance scheme to talk to the insurers on your behalf. What you don't want to do is start the course without telling them as that could be a breach of the policy conditions.
I hope everything works out for you.
Regards
Homer