Backup broadband for business: when your line goes down

When the broadband goes down now, it's not just email that stops. The phones, the card machine, the booking system and the files in the cloud often all run over that one line. Backup broadband for business is a second connection that takes over when the first one fails, so a dug-up cable down the road doesn't close the office. Here's what the options are, what actually switches over by itself, and how to tell whether you need one.

The short answer

• A 4G or 5G backup router is the usual choice for small offices. It sits next to your main router and takes over automatically when the line drops.
• A second fixed line from a different provider is good if mobile signal is poor, but only helps if it reaches you by a different route.
• Starlink works well as a backup on rural Norfolk sites where the mobile signal is weak too.
• Keep the router and phones powered with a UPS (battery backup), or a power cut still takes everything down.
• If an afternoon offline wouldn't cost you much, a mobile hotspot and a plan may be all you need.

Why one line is a bigger risk than it used to be

A few years ago, a broadband fault meant no email for a while. The phones were on a separate copper line and the card machine dialled out over it.

That's changing fast. The old phone network closes on 31 January 2027 (our switch-off guide has the details), so phones move onto the internet. Card machines, alarms and franking machines are following, which our guide to alarms and card machines after the switch-off covers. Add Microsoft 365, cloud accounts software and online bookings, and one line now carries almost everything.

Faults happen to every type of line: a digger through a duct, a car into a cabinet, water in a joint, a fault at the exchange. Most are fixed within a day or two. The question is what that day costs you.

Backup broadband for business: your options

4G and 5G backup broadband

A 4G or 5G router with a business SIM is the simplest backup. Your main router and the backup are joined so that when the main line stops responding, traffic moves to the mobile connection by itself, usually within seconds. When the line comes back, it moves back.

The catch is signal. Ofcom's figures for July 2025 show that outdoors, almost every premises in England has 4G from at least one network. Indoors in rural England it's patchier: each network reaches between 77% and 85% of rural premises, and only 57% can get indoor 4G from all four. So it matters which network the SIM is on, and where in the building the router goes. Our 4G backup runs on the Three network, from £19.99 +VAT a month, and we check the signal at your site first. Ofcom's Map Your Mobile checker is a good first look, but a test in the building is what counts, and an external aerial can help where the signal is weak.

A second fixed line

A second broadband line, ideally from a different provider, avoids relying on mobile signal. The thing to watch is the route. If both lines come from the same green cabinet or the same pole, one digger can take out both. Ask where each line actually runs, not just whose name is on the bill. On industrial estates and in town centres it's sometimes possible to get two genuinely separate routes; in a village it often isn't.

Starlink as a backup

Starlink is satellite broadband. It doesn't depend on local cables or mobile masts, which makes it a sensible backup for farms, rural offices and anywhere the 4G signal is as poor as the line. Starlink's own install guide says the dish needs a clear view of the sky: trees, poles or a roof in the way will cause dropouts. Where 4G works well it's usually the simpler choice, so Starlink tends to earn its place where it doesn't.

When a leased line's fix time matters

A leased line is a private fibre line with a guaranteed fix time in the contract. That's a different kind of protection: it shortens an outage rather than avoiding one. If you're already on a leased line, a backup from a different route still makes sense for a business that can't work at all offline. Our guide to leased lines versus business broadband explains the fix-time side in more detail.

Broadband failover: what switches over and what doesn't

Good broadband failover means most staff never notice the line went down. Web browsing, email, Microsoft 365, cloud apps and hosted phone calls all carry on, because they start the connection from your end.

Some things are different on a backup line, and it's worth knowing before the day it happens:

• Static IP addresses don't move with you. A 4G SIM or Starlink connection has a different address from your main line, and often a shared one. Anything that only lets in your office's fixed address (a supplier portal, a remote access rule, a CCTV viewer) may stop working until the main line is back. Starlink's standard service shares addresses, and a public address is only offered on some of its business plans.
• VPNs need setting up for both lines. Site-to-site links between offices, and staff connecting in from home, should be configured to work over the backup too. It's very doable, but it has to be done in advance.
• Calls in progress may drop. The switch takes a few seconds, so a live call might cut off. New calls work as normal.
• Data allowances. If a backup SIM has a data limit, big uploads or cloud backups during an outage can use it fast. A good router can be set to hold back the heavy stuff while it's on backup.

Your phone numbers on a hosted VoIP system live in the cloud, not in the office. So even with no backup line at all, calls can ring on staff mobile apps or be diverted while the office is offline.

Don't forget the power

A backup line is no help in a power cut if the router has no power. Ofcom's guidance on phone lines is clear that calls over broadband stop in a power cut, because the equipment in the building needs mains power to work.

A UPS (an uninterruptible power supply, basically a large battery) on the router, network switch and phone system keeps them running through short cuts and gives you time in longer ones. The phones themselves are often powered from the switch, so keeping that one box running keeps them all going. Laptops have their own batteries, so with the network up, people can often carry on working.

Do you actually need backup broadband?

Not every business does. Ask yourself what an afternoon, or a full day, without the internet would really cost.

You probably need one if:

1. Your phones are on hosted VoIP and missed calls mean missed work.
2. You take card payments that depend on the office internet.
3. Your main systems are in the cloud and staff can't do much without them.
4. You're rural, and a fault could take days to reach the top of the repair list.

You probably don't if you're a small team that can work from home or a café for a day, your card machine has its own SIM, and calls can go to mobiles. A phone's hotspot and a written plan may be enough. We'll tell you honestly which side of that line you're on.

How we can help

We supply business broadband, full fibre, leased lines, 4G/5G backup (from £19.99 +VAT a month on Three) and Starlink ourselves, along with the routers to join them up and UPS units to keep them running. As DrayTek, MikroTik, UniFi and Grandstream partners, we set up the failover, the VPNs and the phones to work properly over both lines, and test that it actually switches over. Ring us on 01362 760100 and we can check what's available at your address while you're on the phone. See our connectivity and WiFi page, or get in touch and we'll suggest the simplest backup that fits.