Mother any distance
A mother-son relationship with the son moving into a new house and starting a new life after leaving home. It's about him getting further away, but can still report back to his mother when she is needed for safety and someone to help. She doesn't want to let go "your fingertips still pinch that last one - hundredth of an inch" but he pushes through the barriers and leaves everything behind at a new stage in his life for everything to go wrong of right: "to fall or to fly".
About the past and trust with someone who has gone through things in the past and has had bad things happen to her so she finds trust in the other character that could be Armitage himself, as who the character in this poem isn't actually mentioned. This evidence is given by how specific the details in the poem are "canary yellow cotton jacket". The jacket itself could be metaphorical towards the end of the poem as the jacket "still fits" even though it has been years since the childhood of the character when the jacket would have fitted originally.
About Batman and Robin. How Robin has moved on since Batman has 'ditched him in the gutter'. Robin takes control and has become what he wants to be, rather than Batman being the boss of him and giving him orders. He doesn't wear the costume anymore "i've doffed that off-the-shoulder Sherwood-Forest green and Scarlett number". He has shaken off Batman along with all the stories about Batman being a father figure to him. Robin is fed up of being thought of as the "kid" now that he is older and hates it when people think he is still Batman's sidekick.