I am now pretty convinced I did have it at the beginning, before there were tests for public outside hospital - FWIW now. I've heard of several people having positive tests with the symptoms I experienced (fatigue, achiness, sore throat on and off for fortnight). I was travelling for 1.5hours a day, four days a week on the tube leading up to that point, so I was in a pole position to catch it early, especially given I do catch everything.
In laws had similar symptoms end of last month, and my sis in law, who is in a bubble with them, has just had a positive test so her parents - who were in denial at the time - have decided they must have had it after all. So that's good, as they're over 70 and now they've had it so they should be safe in the period until they get vaccinated - which, as mentioned above, might be a moot point now, but then they didn't have a test so they probably should JIC.
I don't know why they don't mention fatigue specifically as a core symptom to be tested after? IIRC it is the one symptom reported by the most people ( >80%), more than coughing or fever, and viral fatigue is quite distinctive from ordinary tiredness, so I don't think you'd get loads of people going for a test because just haven't slept well.