Summary
Minimum guaranteed speed is the personalised speed promise that matters most when a fixed broadband service underperforms. Capture it before ordering and test by Ethernet if you need to challenge performance.
Definition
Minimum guaranteed speed is the personalised line speed an ISP gives you at sale. For providers signed up to Ofcom’s broadband speeds code, if the service falls below that minimum and the provider cannot fix it within the required period, you may be able to leave without penalty. Use it as a practical buyer check: save the written speed estimate, compare it with your needs, and test performance using Ethernet rather than Wi-Fi before raising a fault, because poor in-home Wi-Fi can hide the real access line performance.