To answer your last question first, a comfort letter does not have the force of law. You people have the force of law, and until you enact it, they are only comfort. That's why they're aptly named.
The thing that's very good about the system we have, Ms. Nash, is that over history it's been shown that when the Department of Finance issues a comfort letter and they can explain it to Parliament, Parliament almost always enacts it. I don't know that I can think of one instance where they haven't.
The purpose of the letter really is to provide comfort for an organization to know that the law will be changed, and that if they do something or if they've done something, they won't be on the wrong side of the tax law.