you have to give minimum 7 days notice before you travel.
If you lost a passport and had to get an emergency replacement, it would probably be unwise not to email your PPU team with the new details.
When you are abroad, you are under no obligation to report additional flights made before you return and don't have to give notice of them, although you might want to anyway so as to be seen to be honest. The passport itself contains no details of your record. The chip on the passport only contains digital versions of your photo, signature and personal details. Only UK passport control can see that you are subject to travel notifications, and not even see why (you might be a football hooligan, or a spy). Other passport control in other countries can't see anything about your record unless you have been flagged on interpol. You won't be flagged on interpol unless your crimes specifically involve travelling abroad to commit crimes or you've otherwise given police a reason to suspect you. Or if you've not declared your travel in advance properly.
For example, you go to Hong kong declaring a 180 days stay on your notification which is the max visa free stay for a Brit there. While there, you go to some other country at short notice. and another. and another. None of the intermediate flights need to be declared. No warning will be on interpol.
When you return to UK, passport control will ask if you if went anywhere else, and check the pages for stamps while you answer, so answer truthfully. If you didn't drop your PPU an email to tell them what other trips you made then you can expect them to call you to ask a few questions about what you were doing. But ultimately there's nothing they can do to stop you or penalise you, assuming you returned on time or otherwise emailed them to say your changed your return flight, if you also did that.