I've heard them in the night also, ( for the same reasons as you). Sometimes it's simply because something disturbs them, & there might also be lights on, street lights or even security lights etc. This stimulates them to sing as if it were dawn. Have only read this explanation, don't know answer for sure.

I've heard them tweeting too, late at night when I've been out with the cat! Or just looking out the window before bedtime, you can hear them at times. I think Josee could be right with her thoughts.

It could be a night warbler or something similar, I think there are several species of them. They used to be common in the village where I grew up and that was in the days before street lights came there. They'd be chirping away at 1 or 2 o'clock ...

I am also a hopeless insomniac :(

Edit -
I've just read these birds sing at night :-

Corncrake.
Dunnock.
Nightingale.
Nightjar.
Reed warbler.
Robin.
Sedge warbler.
Song thrush.

.

Thank you all, you’ve put my mind at rest. Thought I was going mad but your explanation makes sense. I shall enjoy the bird song next time and not be freaked out by it!

Just be thankful it isn't rooks....

That’s true Steragram! 😂

they often 'chatter' as a way of reassuring each other. Also if you are outside they will be aware of you and alerting others of your presence. But quite a few birds if they wake up will have a quick sing before settling back down. I guess in a way if they sing 16hrs in summer they will still want to sing 16hrs and just coz its dark that wont stop them. after all they dont have lights like we do so we can stay alert.

So true Seaburngirl. Am lucky enough to live where I do where there are a wide variety of garden & wild birds. They bring so much joy.

Either a danger reaction or noise/light pollution I would think for those species that don’t do that sort of thing at night.