Not a problem, but just one those things that make me wonder. If the previous owner of my TD5 has disabled the seatbelt warning, how are they likely to have done it? The dash warning light for the seatbelt illuminates at startup so I know that works. Should the TD5 beep as well if the seatbelt isn't inserted?

No
No chimes in the UK market but can be programmed to chime via Nanocom and others
I did it but it was annoying so turned it back off