And with a Business level service you get a Business level response for repairs/breakdowns/compensation etc, not a residential service level response which if you are working from home can mean that you will NOT be working from home for quite a few days.
I have never known BT to go out of their way to detect people using their residential phone or broadband services for the occasional work-related reason. I don't suppose they care either way if you use your broadband to upload a few files to a small business web server, or check your emails.
But if you complain loudly on a public web foum that you're losing business because your residential service isn't working, then you shouldn't expect too much sympathy (and even less compensation) from BT.
The other point I sometimes make is that residential services effectively have no Service Level Agreement. Openreach will try to locate faults within 3 working days. But that's not guaranteed. Nor is it guaranteed that they will fix the fault immediately when they find it. If you really need a reliable connection for your business, you should be prepared to pay for a service that does come with a SLA.