I too was living in the Uk and was put on Zopiclone for insomnia. for me it:
1. didn't work, still wide awake 3 hours later, but TERRIBLE hang-over feeling next day after I finally got to sleep from exhaustion
2. Yes horrid metallic taste in mouth - it's a known and documented side effect
3. after 1 week of being on it I had double vision for the next 2 weeks even after I stopped taking it.
I prefer whole-heartedly Temazepam (Restoril in USA) although you will be lucky to get a doc to prescribe it for more than 10 days,and IF you can find it online (I can't) it WILL BE VERY expensive. Temazepam knocks me out after about 1/2 hour and no hangover feelings as long as you are in bed for like 8 hours.