OK so far here is what I have found (on the LH side head anyway which was the side where most of the coolant was coming from) - obviously these are just my theories but seeing as my experience with diagnosing engines is at best very limited someone else my have a better idea so I'm all ears....
As you can see from the arrows it appears for whatever reason there is corrosion of the block and head right near the water jacket which when hit with a sudden jolt of 2.5bar pressure has given way sending coolant into the cylinder. There are no obvious cracks on either the head nor the block (which is a relief).
Question is though - would this corrosion of the block/head cause what has happened or is this just normal wear & tear corrosion that is to be expected in any engine and if so then I'm barking up the wrong tree.....
The head gasket itself is warped around those areas too which I would guess would be where it has leaked. And a straight edge test of the block and head surfaces doesn't seem to show any signs of warping.