The Forster energy transfer mechanisms in polyfluorene-based polymer blends have been investigated by picosecond time-resolved photoluminescence spectroscopy. Blends of poly(9,9-dioctylfluorene), (F8), and poly(9,9-dioctylfluoreneco-benzothiadiazole), (BT), ranging from 50% to 0.01% BT have been investigated from room temperature down to 12 K. In high concentration BT/F8 films, nearest neighbour transfers from F8 to BT, characterised by an F8 fluorescence lifetime of 12 ps, totally dominate. In low concentration BT/E8 films energy transfer between F8 and BT still occurs at nearest neighbour sites, but exciton migration to these sites amongst F8 chain segments now also contributes to the measured dynamics.