If there was enough seperation to allow me to slot in the number 1 position and land without causing the other pilot any delay then that is what I would do informing the ATC (Info) of my intensions however if I thought that by doing this I would delay the other pilot or at worst cause him to go around I would fit into the number 2 position behind him/her regardless. This sort of thing has happened to me a couple of times and is very annoying but is usually a genuine error of judgement by pilots that are unfirmiliar with the airfield.