My experience
Last summer for the first time I needed assistance to get around the airports I could still walk, but only short distances.
We were flying outbound Manchester - Heathrow - Berlin and returning Vienna - Manchester
Manchester : Taken by wheelchair through security left in a designated area in departure lounge and then taken to aircraft for boarding. All good
Heathrow : No wheelchairs on arrival for me or the other 3 passengers needing assistance. We managed to walk part way up the air bridge to a row of seats. After about 30 minutes of waiting I decide to walk the rest of the way into Terminal 5. The glass doors were locked and a member of staff on the other side mouthed to me and my wife " what are you doing there?" . Her pass would not open the door so she had to get a colleague. I explained that I'd been waiting for a wheelchair so she said she'd go and get me one, to which I said " and what about the other 3 who are waiting down the air bridge". I decide to struggle on without a wheelchair. Absolutely shocking!
Berlin : As I left the aircraft there was a wheelchair waiting for me. The young lady had my name and she took me through security, to baggage reclaim and the out to a taxi. Brilliant service
Vienna : couldn't find the assistance desk but I was able to make my own way to the gate. Prior to boarding my name was called and I was taken to the aircraft along with another passenger and boarded the the aircraft before all other passengers. : All good
Manchester arrival. Wheelchairs waiting on arrival for me and the other passenger. Taken through arrivals, baggage reclaim and out to the bus stand for the car park buses.: Excellent.
So of the airports I travelled through the only bad experience was at Heathrow.