Where I once lived, I often heard a bird chirping in the middle of the night. I found it very annoying :o( I was told it was a night warbler.

Possibly thrushes setting up their terratories. I get several at work when i go in at about 6.45am and it's pitch black.

Singing their little hearts out they are and very nice to hear on dark gloomy mornings

All these outdoor festive lights! Never gets dark.

Both robins and blackbirds sing at night. They usually start doing it just before Christmas, or in December, and carry on through January. Robins are starting to think about mating, not sure why blackbirds do it, maybe a similar reason. I've even seen the robin feeding on the bird table at 3.30 am after a good sing along on cold nights.

I spoke to my ornithologist brother in law last night - I already knew robins were territorial, but both male and female robins announce their territory by singing, and usually will do so from December onwards in the middle of the night. Blackbirds also are announcing their territories, but don't sing nearly as often at night as robins do. Excessive night lighting may encourage robins in particular to be more active at night.