there are many theories but i think the ending is whatever you interpret it to be, i don't think there is a definitive end, someone said that sam did actually physically wake up and take the dive of the building and the radio said "we're loosing him, he's arrested" and when we saw him making notes through a Dictaphone, those notes are sent to the female psychologist who goes back to 1981 and to gene hunt, so gene hunt is in the mind and that was what has created Ashes to ashes, that was one theory i heard, quite interesting