Yippee! After my own fiddling around and a few decent size garages having a go the small, one room, one man and a lad outfit have finally cracked it. These guys openly admitted they had never done one, (the others claimed they had) but they took two hours to get the bonnet open by removing the catch securing bolts. This included fitting my new cable and topping up the oil, water and wash bottle. Total cost £60 which I think is money well spent if it preserves your sanity and bonnet. Given my age and old joints I could never have done it and probably would have resorted to the angle grinder method of bonnet sculpture. We all agreed the job was impossible from the front due to the security plate blocking access (now removed) and access from below involves loosening the radiator cowling and having long thin arms. Now all I need is a new plastic grill which was a casualty early on. Thanks to all who advised. Glad I found the forum!