Thanks VERY MUCH INDEED Ixtab! The voice files on the link you posted a link to are different (less files) than the files I'd downloaded from other links (which must have been for other Kindle models). These files worked immediately, thanks very much (and sorry for frustrated post!).
Like most people who have just bought a Kindle and who want to make them work properly for their country, I'm NOT a Kindle expert. So sorry to all the members here for my clear lack of Kindle expertise, which clearly caused some frustration. I'm very grateful for your help.
So for
people with Kindle Touch in the UK who want to change the American Text To Speech (TTS) to a British voice, download the 2 (male/female) GB voice files from here:
http://ge.tt/9XeUvcC
Plug in your Kindle Touch, navigate to tts/data and take the files from inside each of the 3 folders (common, high-quality and low-quality) for the male, and then female, voices and copy them INTO the correct corresponding folders on your Kindle Touch; clicking 'yes' to overwrite the existing files.
(If you want to keep the American voices for future use, just copy the data folder onto your desktop BEFORE you overwrite the files, so you can add it back in at a later date).
Then go to Home, Settings, Menu and Restart your Touch and the United Kingdom voices should now have replaced the American ones.
Despite being a tenth of the size of the American voices, the quality of the smaller GB British voices seem to sound just as good.
Despite being British voices, the procedure is apparently exactly the same for all international tts voice packs for the Kindle Touch.
Thanks again to Ixtab and the other members on this page who helped with this solution!!