I'm a complete novice, so forgive me if I've misunderstood your question, 2Charlie, but I battled with a similar challenge (switching between my work OneDrive and my personal OneDrive) and thought I'd share my solution:
If your employer uses "Office 365 for Business", then your work OneDrive will actually be "OneDrive for Business". Your personal account will be just "OneDrive". Whilst they sound the same, in reality, the two products are as separate as, say, Dropbox and Box.
On your laptop/desktop, this actually has an advantage: You can install two separate Apps from the Windows Store; "OneDrive" (and log in with your personal account details) and "OneDrive for Business" (and log in with your work account details).
The result in Windows Explorer is that both accounts are shown and you can even drag and drop files between accounts. See screenshot attached.
Regarding the mobile/tablet OneDrive app, I think I'm right in saying that you can either install two separate apps (as with the laptop/desktop approach), or, just install the "OneDrive" (personal) app, which now allows you to add a "OneDrive for Business" account.