We could not open door. It has a push on push off rectangular 'button'
on the front. It looks like the control panel or its fascia will have to
be removed to get to the latch mechanism.

For the life of me I cannot see how to do it and am fearful the brute
force and ignorance is not the answer.

Any experts out there?

As a bye-the-bye I did solve the damaged Neff Oven button problem.

First obtain a can of beer.
Next strip off the top and bottom and straighten out alluminium.
Cut a piece to the shape that corresponds to the flat part of the 'D'
shape of the spindle to which it is to be attached.
Glue the piece alli to the knob so that a 'D' is recreated.
Back fill with Araldite so that it will not move once cured.
Re-attach to oven after 14 hours or more.
Enjoy second beer to celebrate.

You just save £23 for a knob that should have cost 10p!