Would anyone know what this is?

Hello! I’ve tried googling but to no avail of what this structure next to a still in use old steam train railway could be, i’m curious as to what it could be / was used for if anyone knows, thank you. This is in the UK if that helps. I apologise for the bad quality

Hello! I’ve tried googling but to no avail of what this structure next to a still in use old steam train railway could be, i’m curious as to what it could be / was used for if anyone knows, thank you. This is in the UK if that helps. I apologise for the bad quality