non-live content was fine
however i can assure you that when i watched it live via iplayer the quality was sub-SD.
One point worth making is, whereas iirc iPlayer used to have HD/SD in settings, these days it is meant to auto adapt. That is, if I have it right, if it thinks the data rate won’t sustain HD, it falls back to SD.
Bear in mind that even if you have a full 80Mbps, or even fibre broadband, if your TV were connected via imperfect WiFi rather than wired, or even with wired if your router or switches were saturated, then iPlayer may decide to fall back to SD.
But speaking as a person who commented “me too” on a recent “I hate football” thread, I can offer no direct experience of this particular phenomemon.
Having said all that, I do often find evidence that the Beeb’s servers are sometimes bandwidth limited.