I guess you have had a look on RRSPORT.CO.UK forum to see if any info ?

@kds I did not, but I did check and no success. Thank you for pointing me to them.

So, it is fixed now... I tried again to open it via the number plate lights, no success. Once opened, I had a look and realised that I had no chance of doing it how the YT said or via the side light. From the side light, the access is blocked by a plastic wall (see pic, the scratches were my attempts to reach the side plastic pin of the latch).

I had to take the rear wiper unit off, unpin the interior tailgate cover and cut the plastic part of its tip that goes around the lock itself (through reaching between the tailgate itself and the interior trim). Only after that I could take the interior panel off fully. You do need an extra pair of hands. After that you pop the lock via the white pin on the lock mechanism itself (see pic). Luckily, it was just the latch itself that was broken and not any other mechanism, it is just a mission to get to it as you are stuck and you have to damage a bit of the trim to unlock it. You do not really see the damage as it is a small cut so that just the locking hook can fit through. Better fixed than not... Mission accomplished and this is what I did a bit of today...