The ISS is most visible in the night at around dawn and dusk, usually for around several minutes before it disappears out of view.
There will be two or three visible passes on the morning of Christmas Day depending on where you live in the UK. The first will be just before 4.45am but it will only be for a very short time – just seven seconds in the north of the UK and 43 seconds towards the south.
The second pass is more promising, starting just before 6.18am. This pass will last for four minutes 33 seconds in the south and move from west to south-east, at a maximum altitude of around 70 degrees.
It will appear lower in the sky towards the northern half of the UK and last for around a minute less, but here there will be another long visible pass before sunrise at 7.52am.
Check the ISS tracker for your local area here, external or download the NASA app.