When caring for my dad and MIL, I got them both blue badges - or more correctly the doctor said they need one, here's the form I'll sign it. Anyway there are times when you, able bodied driver, can park using a blue badge. The most logical and memorable one is when you are going to pick up a disabled person from somewhere. I can't be sure but it may include visiting a disabled person that you are expecting to pick up, but don't actually collect them. Or, of course, if you have a big BMW because you are making up for your other deficiency in the manhood department, you are indeed disabled.
When my MIL was in hospital dying, as it turned out it was her last night, I drove to the hospital late in the day and parked on a single yellow line outside the hospital - a wide road, not impinging traffic flow. I parked about half an hour before the start of the de-restricted time next to a single upright pole with what may or may not have been a parking restriction sign. The sign was completely obliterated front and back with wide black adhesive tape, which must have taken several minutes to apply so I thought it was official. 30 yards along the road there was a similar pole with restricted parking times. Cars were parked all along this bit of road.
Anyway we were a long time in the hospital because MIL was dying, and indeed she passed away at about 02:30. When we returned to the car with her death certificate we had a ticket. I appealed with a photo of the obliterated parking restriction sign, they said theres a sign 30 yards down the road. I said my MIL was dying and we were visiting her. They said send the death certificate, which I did, and they let me off.