Most businesses have heard of the BT switch-off. Fewer know what's actually being switched off, how many lines are still on it, or why it matters if you're not a BT customer. Here's what I tell clients.
The short answer
The UK's old copper phone network is retired on 31 January 2027. Every phone line, ISDN line, and anything else that relies on it — alarms, lift lines, card machines — needs to move to a digital service running over an internet connection. It affects every provider, not just BT.
What's being switched off, and why
For over a century, UK calls have travelled over copper wires and telephone exchanges, known as the PSTN. ISDN, the digital line behind most larger phone systems, runs over the same network. Both go. After the deadline, calls travel as data over broadband or fibre. You keep your numbers, and you can keep desk phones.
The reasons are practical. The exchange equipment is decades old, parts are scarce, faults are rising, and running a copper network alongside the new fibre one costs money that ends up in everyone's bills. It was first announced in 2017 for the end of 2025, then pushed back to January 2027 after forced migrations were paused in December 2023 following serious incidents involving telecare alarms for vulnerable people.
How many lines are still on it?
Openreach's latest estimate is around 1.2 million lines nationally, down from 1.5 million at the end of July. In September it published a breakdown for the ten largest city areas, which between them still had over 600,000 lines left:
| City area | Lines left | Share not yet moved |
|---|---|---|
| London | 235,934 | 12.9% |
| Leeds | 62,411 | 8.6% |
| Manchester | 55,961 | 7.4% |
| Sheffield | 51,870 | 7.6% |
| Liverpool | 42,351 | 6.4% |
The North is ahead on percentages, but Leeds and Sheffield still have more lines left than Birmingham or Glasgow. London is behind on both counts. And the old lines are getting more expensive to keep: Openreach's wholesale price for them rose 20% in April and 40% in July, with a further 40% on 1 October, taking them to double their 2025 level.
Who's who
Calling it the "BT switch-off" makes it sound like a BT problem. It isn't.
| Name | What they actually are |
|---|---|
| BT Group | The parent company. Owns Openreach, BT Business and EE, and runs the network being retired. |
| Openreach | Owns the cables, poles and exchanges. Sells to providers, not to you. |
| BT Business | One provider among many. Being with them doesn't change your deadline. |
| Sky, TalkTalk, Vodafone, most business providers | Rent Openreach's network. Affected in exactly the same way. |
| Virgin Media O2 | Runs its own separate cable network, and is moving its own customers to digital lines too. |
So talk to whoever sends you the bill, not Openreach. You don't have to move to BT. And if you have several sites, you may have several providers with several different plans. Check each one.
Will it affect our broadband?
ADSL, the oldest copper broadband, is being withdrawn. Most "fibre" broadband (fibre to the street cabinet, copper to the building) moves to a version that doesn't need a phone line, usually at the same speed. Full fibre, leased lines and Virgin Media cable carry on.
The bigger change is that your phones will now depend on your broadband. A single fault or a power cut can take out both. Ask whether you have a backup connection, what happens to calls in a power cut, and whether your main numbers can divert to mobiles automatically if the office goes offline.
What happens to international calls?
This is the question almost nobody asks, and it's where I see businesses caught out after the move.
- Calling abroad still works, but check the price. International calls are often outside the bundle on new digital plans. Read the rate card before you sign, not when the first bill arrives.
- Internet phone systems attract fraud. A hacked phone system can rack up thousands in international calls over a single weekend. Ask your provider to bar destinations you never call and to set a spending cap.
- Calls from abroad showing your UK number can be blocked. Since January 2025, Ofcom has required UK providers to block calls from abroad that display a UK landline number, apart from a few legitimate cases. If an overseas office, an offshore call centre, or a cloud system routed through another country makes calls showing your UK number, check with your provider that it's set up properly, or those calls may never arrive.
- Customers abroad calling you notice nothing, as long as your numbers are moved correctly.
Is anyone else doing this?
The UK is late, if anything. Estonia finished in 2017 and Singapore in 2020. The Netherlands and Germany have moved almost everyone, Japan moved its core network at the end of 2024, and France and Denmark are aiming for 2030. Every one of them found the same thing: moving phone calls is easy. The hard part is everything else plugged into the old lines.
If you're still on ISDN, start with my ISDN guide. If you're wondering whether you need landlines at all, read this first.
Common questions
Is the BT switch-off only for BT customers? expand_more
No. It affects every provider that uses Openreach lines, including Sky, TalkTalk, Vodafone and most business providers. Virgin Media is making the same change on its own network.
Will our phone numbers change? expand_more
No. They move with you to the new service, as long as they're moved before the old line is switched off.
Do we have to switch to BT? expand_more
No. The switch-off changes the technology, not your choice of supplier.
Does it affect mobiles or leased lines? expand_more
No. Neither relies on the old copper phone network.
Line counts from Openreach's September 2026 city figures and national updates. Price rises from Openreach's legacy line price schedule (February 2026). International calling rules from Ofcom's guidance on calls from abroad presenting UK numbers (in force since January 2025).