Thank you for your comments. It's certainly worth keeping an eye on this to see how TTS progresses. If they add voice to navigation it will certainly be an option to buy in the future.
Unfortunately I can't try my friend's Pocketbook as she lives in Italy and I'm in the UK. She is also blind but manages to use it with another specialised piece of "scanning" equipment, which is not only very expensive but now obsolete. She runs the handheld scanner over the screen to read, which then transfers the information to a braille reader which she reads with her other hand. Seems very long winded but she finds it acceptable. As my husband doesn't read Braille it's not an option for him.
Thanks again for the replies.