I agonised over another plant looking like this trying to determine which senecio it is - and decided that the safest option was to assume it was madagascan fireweed
Perhaps it'll be best to pull this one then, Liam I have sent you some information regarding identifying Madagascan fireweed. If you are able to return to this plant with the new information in mind and either provide us with some field notes (number of bracts, petals etc.) or remove the plant, that would be good :).