Slow broadband on a long line: causes and fixes

FTTC stands for fibre to the cabinet. Openreach, which builds and maintains the network that many providers sell over (Plusnet, for example, does not build its own and runs on Openreach), describes it like this: fibre carries the signal from the local telephone exchange to a green street cabinet, and the final stretch from the cabinet to your home is traditional copper wire. Openreach also calls FTTC superfast broadband or VDSL, and thinkbroadband refers to the technology on the copper stretch as VDSL2.

Openreach says FTTC offers download speeds of up to 76Mbps and uploads of up to 15Mbps (checked October 2026). For example, Plusnet advertises its part-fibre Fibre service as "your best available speed up to 66Mb", and BT's Part Fibre packages are FTTC with speeds of up to around 80Mb (both checked October 2026). Our Plusnet broadband deals page shows its part-fibre and full fibre options side by side.

ADSL, which Openreach also calls standard or copper broadband, uses the copper phone line all the way from the telephone exchange to your home. Openreach says it offers download speeds of up to 21Mbps and uploads of up to 1Mbps (checked October 2026).

Because the copper runs the whole way from the exchange, it is your distance from the exchange, not from a cabinet, that counts on ADSL.

Since 16 September 2024, Ofcom guidance has required providers to describe the technology in clear terms such as full fibre, part fibre, cable or copper, not just "fibre", at the point of sale and in the contract information and contract summary. So your contract summary should say which you have. Our guide to what a broadband contract summary must contain shows where to look.

• Part fibre means FTTC: the length of copper from the cabinet to your home matters.
• Copper means ADSL: the length of copper from the exchange to your home matters.
• Full fibre (FTTP, fibre to the premises): thinkbroadband, a long-running UK broadband information site, says its connection speed is not affected by distance.
• Cable (DOCSIS): thinkbroadband describes cable and full fibre as fixed-speed connection technologies, rather than speeds that vary with the line, and says coaxial cable is more resilient to interference than a phone line.

The rest of this guide is about copper-based lines.

Openreach says FTTC speeds can start to drop noticeably beyond around 300 to 400 metres from the cabinet (checked October 2026).

thinkbroadband's fibre broadband guide gives guideline FTTC estimates by distance from the cabinet. Parts of that guide date from 2012 to 2017, the figures are estimates rather than promises, and thinkbroadband says most lines should exceed them. Treat them as a picture of how speed tails off, not a prediction for your home.

Source: thinkbroadband guideline FTTC estimates (VDSL2 profile 17a). These are connection speeds, so compare them with your router's sync speed (explained below), not with a speed test.

On a long FTTC line, a higher speed tier usually will not help. thinkbroadband explains that if a line cannot reach the top speed of a 40Mbps FTTC product, moving to a 55 or 80Mbps FTTC product will not increase the speed, because all of them use the same VDSL2 technology over the same copper.

The line sets the ceiling. Only a technology that does not depend on copper length, such as full fibre, changes that.

Most providers give you a personal speed estimate when you order, either as a single figure or a range. thinkbroadband says slowness should be judged against that estimate, not the "up to" speed in adverts.

If your provider has signed Ofcom's voluntary broadband speeds code of practice, it must also give you:

• an estimate of the speed you are likely to get at busy times (8pm to 10pm for home services), and
• a minimum guaranteed speed, which for superfast products is based on the capability of your individual line.

Ofcom lists the signatories as BT, EE, NOW Broadband, Plusnet, Sky, TalkTalk, Utility Warehouse, Virgin Media and Zen Internet. If you no longer have the figures, ask your provider to send them again. Our guide to the minimum speed guarantee explains how the estimate and the guarantee differ.

On ADSL2+ (a version of ADSL) and FTTC, your router "syncs" with the equipment at the exchange or cabinet when it connects. thinkbroadband explains that the speed it connects at is dictated by the conditions on the line at that moment. thinkbroadband says the figures shown in the router's web interface (its settings pages) are this connection speed. Some provider hubs make it harder to find; if you cannot see it, ask your provider, which can check your line speed from its side.

Your speed test will always be a bit lower than the sync speed. thinkbroadband says real throughput is normally about 86% to 96% of the sync speed, because of protocol overheads (the extra data needed to manage the connection).

Example (illustrative only): if your router shows a sync speed of 30Mbps, a wired speed test of roughly 26 to 29Mbps is in the normal range. A wired test far below that points to something other than the line itself, such as a busy device or software on the computer, or congestion on the provider's network at busy times. Compare with Wi-Fi tests and test at different times of day. A sync speed that is itself well below your provider's estimate points to the line or your wiring.

Ofcom says the most accurate speed test comes from a computer or tablet connected to the router by an Ethernet cable. Separately, its tips suggest plugging the router into the main phone socket where possible, to cut interference.

1. Plug a laptop or computer into the router with an Ethernet cable.
2. Pause big downloads and streaming on other devices.
3. Run a test on our broadband speed test page and note the date, time and result.
4. Repeat on a second device if you can, as thinkbroadband suggests, to rule out a problem with one computer.
5. Test at different times of day. If speeds drop mainly in the evening, our guide on why broadband slows down in the evening covers that separate cause.

Openreach's Full Fibre checker shows whether full fibre is available, planned or being built at an address, or that there are no plans. It gives no speed figures. Other networks build full fibre too, so it is worth checking more widely; our guide on how to check full fibre availability at your address explains how.

You can also enter your postcode in the comparison on our fibre broadband deals page to see which deals are listed for your area, labelled by type.

• Your personal speed estimate and minimum guaranteed speed from when you ordered.
• Your router's sync speed, with the date you noted it.
• Dated, wired speed test results from different times of day.
• Confirmation that you tested at the master socket with extensions disconnected and microfilters fitted.

Ask: is my sync speed right for this line, does it run through a street cabinet, could line management have slowed it, and would an engineer visit be charged?

thinkbroadband notes that a provider may send an engineer but may charge for the visit. Our guide to when you can be charged for an engineer visit explains who is responsible for which part of a fault.

Under Ofcom's speeds code, if your speed falls below the minimum guaranteed speed, the problem is on the provider's network and it is not fixed within 30 days, you can leave without an early exit fee. The right to leave also covers bundled services such as a landline or pay-TV, and since 21 December 2022 it extends to any product linked to the broadband financially, contractually or technically. Rolling monthly contracts are outside this, but can be ended with notice.

Some providers add their own promises. BT, which sells Part Fibre (FTTC) as well as full fibre, has a Stay Fast Guarantee that covers speed to the hub and gives a reward card if speed is not restored within 30 days, with up to four claims a year (checked October 2026). Our BT broadband deals page shows its current part-fibre and full fibre packages. Check any provider's own guarantee in its terms before you sign.

Be realistic: because the minimum guarantee on a superfast product reflects your own line, a long line that is slow but matches its estimate is not a fault.