MK4 Tailgate lock replace Lock Latch

Hi

I have a Mk4 2004 polo and I have a tailgate lock that that will not open by remote or 'hard' key.

Having removed all the internal trim to gain access, I was able to 'lift the lock mechanism' which should open the tailgate, however this does not work. The lever within the latch mechanism just hits against something and fails to open the tailgate, i also note there is a torsion spring hanging out from the latch mechanism.

So the question is - with the tailgate closed how can I release or remove the latch to open the tailgate?

Thanks in advance Andy