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If your broadband is slower than advertised, run a wired speed test at the router and compare the result with the minimum guaranteed speed in your contract. Slow wifi with a fast wired result is a setup problem you can fix yourself. A wired result persistently below the guarantee is a fault your provider has 30 days to fix before you can leave penalty-free.
Every household has a version of the same scene. The package says 150Mbps. The speed test, run on a phone at the wrong end of the house at 9pm, says 23. Someone declares the provider is robbing them. Someone else suggests turning it off and on again. Nobody is entirely wrong. The gap between the number you bought and the number on the screen has about five possible causes and only one of them entitles you to anything.
So here is the workflow. Test properly, find the cause, decide whether it is setup or fault, then use the rights that exist. The fine print of those rights lives in our advertised versus minimum guaranteed speed explainer; this guide is the practical end.
Less than you'd hope. Since 23 May 2018, UK advertising rules have required broadband speed claims in ads to be described as "average" and to be achievable by at least 50% of customers at peak time, defined as 8pm to 10pm. The old "up to" headline speeds, achievable by roughly one lucky customer and a laboratory, are gone.
The catch is in the maths. If the advertised figure is what half of customers can get at peak, then by definition up to half get less. The advert is a median, not a promise. It tells you how the deal performs across everyone on it and almost nothing about your line.
So a test result below the headline number is not, by itself, a breach of anything. The number with teeth is one most people have never looked at.
Providers signed up to Ofcom's voluntary speed Codes of Practice must give you a minimum guaranteed download speed at the point of sale. The signatories are BT, EE, Plusnet, Sky, TalkTalk and Virgin Media, who between them serve around 95% of home broadband customers, plus Utility Warehouse and Zen. Most altnets have not signed, which matters later.
That figure is personal to your line rather than a marketing average. BT's explanation of how it builds the numbers is unusually instructive: it runs SamKnows test agents across a panel of around 35,000 lines, treating 8pm to 10pm as peak. Its full fibre point-of-sale speed ranges then come from the 20th to 80th percentile of panel results. On part-copper lines checked by phone number it uses your actual line speed. The estimate comes from real lines like yours, which is why it carries weight in a complaint.
Your minimum guaranteed speed is in your contract summary, order confirmation or online account. Dig it out before anything else, because the whole workflow hangs off that one figure.
A speed test on a phone in the kitchen measures your wifi, not your broadband. Your rights attach to the speed reaching the router, so the evidential test is a laptop plugged in with an ethernet cable. Ofcom's consumer advice says the same: connect by ethernet for accurate testing.
The method:
Test wired into the router. On a part-copper (FTTC) line, use the master socket rather than an extension.
Pause the downloads, streams and backups on every other device first.
Repeat over a few days and at different times, including the 8pm to 10pm peak.
Use your provider's own checker or an Ofcom-accredited tester when building a case and keep dated screenshots.
Then test over wifi in the spot where things feel slow.
Wired fast, wifi slow. The most common outcome by a distance. The line is fine; the wifi is the bottleneck. Router placement, interference (Ofcom names halogen lamps, dimmer switches, speakers, baby monitors and TVs parked next to the router), too many devices or an ageing router on an old wifi standard. All fixable without a phone call. Start with Wi-Fi speed test: how to do it and read the result to map the problem, then How to speed up your broadband for the fixes.
Slow everywhere, matching a modest estimate. Copper physics caps a part-copper FTTC line at roughly 80Mbps even in ideal conditions; a line 500 metres from the cabinet is doing well to manage 40 to 50Mbps. If the wired result matches the estimate you were given at sign-up, the line is delivering everything it can. The fix is a faster connection type, not a complaint, so FTTP, FTTC, cable and 5G: broadband types explained is where to head next.
Fine at 11am, crawling at 9pm. Peak-time congestion. The advertised average is measured between 8pm and 10pm, so a connection that drops below your guaranteed minimum every evening is exactly the case the code exists for.
Slow everywhere, below the guarantee. Now you may have a genuine fault. On to step three.
Wired speed at or above your minimum guaranteed while the wifi struggles: that is your setup. No code rights apply, so fix the wifi with the guides above.
Wired speed persistently below your minimum guaranteed: report it. Under Ofcom's 2022 code, in force since 21 December 2022, a signatory provider then has 30 calendar days to fix the fault. If it cannot, you can leave penalty-free, including any landline or pay-TV taken in the same bundle.
A dead connection is a different scheme entirely. Total loss of service triggers automatic compensation of £10.34 per calendar day once you have been offline for two full working days after reporting it. Slow speed alone never triggers automatic compensation, however dramatic the slowdown. Do not let a call handler conflate the two.
Provider not a signatory? Most altnets are not. There are no code rights to invoke, so your route is the contract terms, then the formal complaints process, then ADR.
If a complaint stalls, you can escalate to ADR after six weeks (for complaints raised on or after 8 April 2026) or sooner if the provider issues a deadlock letter.
When you do report it, wording matters. Try: "My minimum guaranteed speed is X. My wired tests on these dates show Y. Please log this as a speed fault under the Ofcom code of practice." Dated, wired, specific. Retention scripts have no good answer to it.
Most slow-broadband stories finish at step two, with a router moved off the floor and a Sunday evening recovered. If yours reaches step three, the 30-day clock is your lever and our rights explainer covers the exit itself in full. And if the wired speed was healthy all along, the problem may simply be a package the household has outgrown; What broadband speed do I actually need? puts a realistic number on what to buy instead.
Because the advertised figure is an average that only half of customers need to achieve at peak time. Add wifi limitations, distance from the cabinet on part-copper lines and evening congestion. A wired test against your minimum guaranteed speed tells you whether anything is wrong enough to act on.
Yes, if your provider signed Ofcom's speed code and your wired speed stays below the minimum guaranteed figure you were given at sign-up. Report it, give them 30 calendar days and if they cannot fix it you can exit penalty-free, including bundled landline and pay-TV.
Not for slowness alone. Automatic compensation pays £10.34 per calendar day for a total loss of service lasting more than two full working days, plus fixed amounts for missed engineer appointments and delayed starts. Slow speed is handled by the 30-day fix-or-exit right instead.
Not for complaint purposes. A wifi test measures your wifi as much as your line, so a provider can wave it away. Test with an ethernet cable into the router. That wired result is the one your minimum guaranteed speed is judged against.
The advertised number was never a promise, but the one in your contract is, so test the line and hold someone to it.
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