Hi @barryjones
You can add your accountant as a new team member (regardless of the subscription), by going to Account Settings > Team Management.
However, we do operate a one account per email policy, so if your accountant has another account he uses, you won't be able to add them. In this case, they should look at signing up at our Affinity platform which is aimed at accountants who manage multiple accounts.
I hope that helps!