You should be able to use with and without the PEX number according to the notes on the TNT tracking site. I’ve tried both and they show an error.
I called the passport helpline and they put me through to Urgent update team. They were helpful and sent an urgent message to the processing office for it to be sent today for next day. I’m dependant on someone at the processing office to pick that up and action it though. They also suggested I call TNT just in case they have it which I did but they confirmed they don’t have it yet. TNT collection is at 4.30pm daily. I was advised to keep checking the tracker online and if that shows my details then call back to TNT to get them to upgrade to next day delivery for tomorrow. There is still a chance it could arrive in time for our flight on Sunday but very little for anything to slip.
Will update again after 4.30pm to see if got picked up.