Here's an update on the harness training so far...
Training has been a bit limited recently because I was in the process of redecorating half of the house (all three bedrooms and hall/stairs/landing). This meant the cats had to have their litter trays and food moved downstairs to where Alfie is. As a result I had to limit Alfie's out of cage time to make sure the cats weren't bursting to use the tray or missing out on food. I didn't focus on the training too much during his out of cage time, just let him fly around and get as much exercise as possible before the cats woke up and wanted to come downstairs. However, I did make sure to get the harness out pretty much every day and ask him to put his beak through the bars and through a hoop to get a treat. This was pretty easy for him as it was only ever his beak coming through the bars, but it allowed me to familiarise the words 'head through' and the action of putting his beak towards the hoop to get the treat.
Things are (almost) back to normal in the house now and the cat stuff has all moved back upstairs. The last few days I allowed Alfie just to play and fly around as much as he liked to get used to having the extra time out of the cage again. I carried on asking him to put his head through when he was in his cage and now I'm starting to work with him out of the cage too. Yesterday I asked him to put his head through the large loop three times - then he wandered off to play so I stopped the training.
Today I let him out, let him fly to his shelves and settle down then grabbed the harness and 5 cedar nuts. I managed to get him to repeat the behaviour 5 times (giving him a nut each time) AND I was able to make the loop a little smaller each time. Now that he's training out of the cage I am asking him to put slightly more of his head through. He was a little hesitant a couple of times but I didn't force it, just kept the loop and the treat in place until he was ready to lean forwards. I'm letting him come to the treat each time. A couple of times I managed to move the harness back ever so slightly so more of his head was going through. He also brushed the harness with his head a couple of times.
Again, not a major update but I am being very cautious and not forcing the issue at all.