If you are a Business or someone who's job is internet based it is is essential that you have some fail-over in your internet connectivity.
As more and more job roles or project outcomes rely on information being issued online, whether by email, submissions to a portal, or electronic ordering and tracking, it is often imperative that this is done by a certain deadline.
Whilst some situations will allow for flexibility in this and people will understand if you have 'internet issues' others such as payroll or tax related functions, or issuing of contract specific project information may not be so flexible.
Both in my business life and on a general basis I would recommend that if your work relies on the ability to send or recive information online, to a deadline, you must have a backup connection.
In the UK that would usually be a combination of a BT Broadband Service and one from another supplier. Take care to ensure that your secondary supplier is not simply a re-branded BT service otherwise it's not really a backup. A combination of something like BT and Virgin would be a good option, especially if you can have both services on Fibre connections for the speed benefits that brings.
Most modern business routers will be able to support dual connections. They can automatically switch traffic in the even of one connection failing, and manage the bandwidth between the connections to ensure the best service.
Having two connections means if there is a broadband outage on one service you should still be able to work, send emails and get that document issue in by its deadline.
Depending on budget you can either have two high spec connections or keep the backup service on a basic package. The main thing is to have one, the small additional cost to keep operational during an outage will quickly pay for itself.