As
CR001 has mentioned above, it is the naturalisation certificate that is proof of your British citizenship, not your passport, which is only a travel document.
There have been cases where children who were issued British passports were denied renewals as it was subsequently determined that their parents had not met the requirements at the time of birth of the children. So renewals are not automatic.
Also, in some cases, your children and perhaps even grandchildren, especially any born outside the UK, may need to prove that you were a British citizen
otherwise than by descent. The
only proof of that is your naturalisation certificate.
And remember that the onus is on you to keep/maintain your data, not the Home Office's
And there is no centralised database of British citizens. If you need to prove your British citizenship,
you will need to produce the naturalisation certificate.
Also see
this thread discussing how long to preserve the documentation proving your immigration process, never mind just the naturalisation certificate.
I am not a lawyer or immigration advisor. My statements/comments do not constitute legal advice. E&OE. Please do not PM me for advice.