@Rachael thank you. That gives me hope.
Have you tried bottoms with no pants? I had the same with my girl when we potty trained, pants felt too much like a nappy so we just went without. Nursery were happy to accommodate this too, think after a week she was fine with pants. I know a girl is different but maybe joggers would be comfortable for him?
My boy was exactly the same, I had to keep him bare bum for a good 5 days before we could try pants. Every time I put pants on him he would wee in them, I think he thought it was nappy and couldn’t decipher between the 2. He’s now been potty trained for a few months and doesn’t have many accidents, but he did go back and forth for the first week or so!