Lost and Found (UK Passport) & SLTD database

I previously misplaced my UK passport which I reported lost and the passport was duly cancelled. I have since found the passport.

I have two questions:

(1) What should I do with the ‘lost’ passport. When I spoke to the Passport Office, they said that if I were to find the passport I didn’t need to return it. They said I should cut the top corner off the passport. However, the email I got when I reported the passport lost asks me to post it to the passport office but no details beyond that.

I’m worried that the passport may get lost in the post, which is obviously worse for me from a fraud perspective. It isn’t clear whether the passport office will confirm receipt of the passport or return the passport to me afterwards. Does the passport get returned? Should I send the passport recorded mail and track it’s progress?

(2) The Passport Office says that it passes the details of the lost passport to Interpol and it is now in the SLDT database. Are only my passport number and country of passport stored on the database? It’s clear that these details are cross-checked by authorities, but does the Passport Office pass further information e.g. Name, DOB, picture to Interpol? I’m not sure I want more detailed information to be potentially accessed by 3rd parties. Can I request for this data to be removed if I return the ‘lost’ passport to the Passport Office?