@Alex Atkin UK:
You might have better luck removing the PoE splitter from its plastic shell
Yes, certainly another option I hadn't thought of, would have to cannibalise the case, appears to be glued together, wouldn't worry too much about the warranty as the splitter didn't cost a fortune.
Had a bit of a shock yesterday morning, ONT LOS red LED illuminated, PON green LED out, obviously no BB or digi LL phone service.

As replacement of the ONT power source was the last significant event, decided to re-instate the original ONT PSU in the unlikely event that this had somehow effected or even damaged the Nokia ONT, left installation as original for further OR remedial activity.
Contacted BT who advised that an engineer would attend today, Saturday AM.
OR engineer attended @ 08:30 hrs and re-made the fibre joint at the CSP box fully restoring service.
Nice lad, even removed his shoes at the front porch!
He related that fibre joint failure was not uncommon, in this case the original joint made by the OR sub-contractor may not have been 100% even though it read healthy at the time of installation.
Ironically with many years of ADSL/VDSL BB service I have never had a complete outage as such and have now experienced a 24 hr BB & phone outage within a week of the FTTP installation!
Can't complain about the BT/OR remedial service especially on a Saturday, made sure to submit a favourable review for the OR engineer.
Being satisfied that the ONT PoN power supply had no bearing on the failure will re-instate after reviewing some of the options suggested.