OK, I called Pro Honda this morning and explained my predicament. A very helpful chap there called Ray took my mobile number and said he'd get back to me shortly. He rang back about 45 minutes later to tell me that although Honda don't do replacement keys, they do sell replacement lock assemblies...for $22!...and he happened to ahve 1 in stock that he'd had for about 2 years. I let out a small cheer, grabbed my car keys and took off.
Home again 1 hour later with new lock Assy (+ 2 keys). Took me about 20 minutes to complete the job. I removed enough screws to get sufficient access to the inside of the handle and latch, held it all together whilst I removed the retainer washer, spend 5 minutes searching the garage floor for the steel ball bearing which provides the tension which had dropped out when I pulled the old bits out. Found it, fitted it, held it all together and pushed the retainer washer into place. Job done!! Reassembled the handle assembly with the 4 retaining screws and lo and behold it works!! New key, no bother.
Yippee!!!