I suspect you will find that if you check your contact, you have no service level agreement that makes a premise of a certain level of uptime and therefore no right to compensation for an outage.
SLAs are typically only available with expensive dedicated corrections such as leased lines. "Business" broadband almost always has better Openreach time to repair for line faults than a residential line, as well as enhanced customer service, but that's about it.
If internet connectivity is business critical, you should always have a backup connection, ideally with as little as possible in common with your main connection. For emergency use, mobile broadband might be suitable.