Bird singing all night, at this time of year. Why? And what might it be?

Last night a bird was singing in a tree across the road from my house, from about 2.30am to at least 7. It's done the same for the past several nights, except starting more towards 4 or 5am, and it was the same about this time last year.

Does anyone have any idea what it might be, or why the free night-time Christmas concerts? I live in Lancashire in the countryside. I would say the song was remarkably beautiful, like an extended improvised flute solo. It went on all night with very brief intermissions. Thanks if you can help.