A voice fileset should consist of between two and four files
the two essential ones are:
dataxx.chk
dataxx.vif
(where "xx" is a two digit number (or can be three digit on later models))
and you can also have
dataxx.bmp - a picture of the voice person
dataxx.tlv - an index file used by Home only.
Each voice needs a UNIQUE two digit number so if you have added any there might be conflicts.
Using Windows Explorer on your PC, check to see what files you have in the "voices" folder on the TomTom's SD card.
The standard UK voices are "Tim" - data04 and "Kate" - data 05 so there will probably be 6 files for those (no .bmp)
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Also,, if you have downloaded the new voices from another site, there's absolutely no need to use "Home" to add them, just copy the files above into the voices folder yourself manually.
But if you need to change the numbers of any of your added ones, report back, because you can't just change the number in those file names you also need to edit the .vif file too (an easy 2-minute job, using Notepad).
If you let us know where you got the voices from (with a link), we can give some more specific instructions.