Song thrush are certainly singing a lot in the northeast at the moment, frequently at 7am and often much earlier (I was listening to one at around 4.15 hrs a few days ago). The repetitive nature of a song thrush's song is usually the 'give-away', they can make (and repeat) a wide variety of sounds, including mimetic ones. So, listen for the two or three-times repeated song phrases (or notes), rather than just the sound of the notes, which would indicate that you are correct.