There's something wierd about this. I deleted all events that were linked to the second place 'Harpurhey' (the one that showed up in red in the places list) and it disappeared from the places list as expected.
I recreated an event for one of the individuals and selected 'Harpurhey' from the drop-down list. Opening the places list I see there is only one 'Harpurhey' listed but this individuals event isn't linked to it - instead it is linked to an unknown place at the top of the places list. I think the screenshots might explain it better!
I'm guessing that because the lat/long co-ords for Harpurhey are showing in black rather than blue in the places list, it is not considered a valid place and new events are therefore being linked to the 'unknown' place.
Can someone explain this please or tell me what I'm doing wrong, it's very confusing!