So I’ve lived in this flat for a year and a half and only had my CO alarm go off once randomly and never again until yesterday. Yesterday and today it will beep a few times (sometimes 3, sometimes 4 or 5) and will continue beeping for a few minutes then stopping for hours before starting to beep again? I have tried searching why this might be because everywhere I’ve looked said if it stops itself then it can’t be detecting CO because otherwise it would keep beeping? What is causing this? What can I do?

As you note, a carbon monoxide detector will sound when it detects carbon monoxide and stop shortly after there is no carbon monoxide present. Since the detector in question has been problem free for most of the time, it could be one of two possibilities.

1) The detector is nearing the end of its useful life. (You do not say it's age)

2) The detector is actually detecting carbon monoxide (Have you or any of your neighbours had anything new / started to use a heater?)

Since carbon monoxide is colourless and odour less, you could buy another carbon monoxide alarm (With digital counter would be preferable) place it adjacent the existing carbon monoxide alarm and monitor what happens.