Thanks fellas! i managed after another hour to get it open, got in from work dreading the job and tried every thing to get it open but still could not get it to shift. I was fortunate that i did not put the grill in and was able to reach the stays by hand, tried as recommended pulling cable but it would only free the drivers side. I even removed the front bumper but! had no joy with that either. Eventually, and with brute force i managed to pop it!
My heart was in my mouth as i was waiting for a loud crack but thankfully it never happened!
So! for anyone replacing their bonnets on their GTV/Spiders, i recommend
1.) Only very loosely bolt bonnet to hinge and ensure that you can move it forward and back and side to side.(But! be carefull as you need to push in towards centre of car when bolting bonnet in order to form a bow effect and give enough clearance of cars bodywork)
2.) Mount the struts. (they help to centre the bonnet)
3.) Loosen the bonnet stays on the bonnet.
3a.) Remove Grill.
4.) Slowly lower bonnet and closely examine the bonnet stays are plumb with their securing holes, this is why you loosened them.
5.) Check the bonnet gaps and make sure it is square. Raise gently again and tighten one bolt on each side of the hinge. Check again it is square without closing.
6.) Say a prayer and gently close bonnet.
7.) Pop it again and tighten stays and mount struts and all other hinge bolts.
Bobs yer Uncle!
PS: If anyone needs any of the bits & bobs that are mounted to the bonnet let me know,eg: seals, stays, headlight foams, sound deadening blanket and grommets etc, i stripped them of the damaged bonnet and they are all in good nick, seemed a waste to bin along with cracked bonnet.