For those without TNT tracking or if its not working, another provider might have been used. I received my passport today via DHL, only got the text this morning with tracking information. It’s totally different to your PEX number and it was UK mainland delivery.
I stumbled across this a few days ago: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1012937/Passport_printing__V1_.pdf
