I followed a number of excellent guides which recommend making a thin tool bent at 90' to push back the spring and allow the ply to be removed but no matter how I tried, I could not push the clips back enough to withdraw the plywood mounting. I think the plywood is not original and is too thick preventing the tool from being inserted properly and the clip being too tight on the thick plywood to allow any movement.
I then found further advice which suggested drilling two holes in the surround to allow the spring clip to be pushed back with much more force.
This did the trick and I managed to remove the whole headlining.
The technique is to insert a very thin but blunt steel ruler or something similar and gently slide sideways between the metal surround and the headlining to locate the exact locations of the spring clips which are about 10mm wide and about 300mm from the A Posts.
Mask off the window surround and mark the location of the clips. Use a centre punch to mark then use a stepped drill to open a 8 - 10mm hole.
You should then be able to see the clips. I used a screwdriver to push and lever the spring clips back and allowed the plywood to slide out. It took a lot of force and a bent tool would never have worked in this instance.
Some may not want to drill holes but I had no choice and am sure will be able to make it look fine by using a blind grommet and will also make access much easier if this has to be done again
