Thanks for the tip Casper27. I hadn't looked at the new voice options in v10 and 'Simon' sounds okay compared to v9's 'Lucien' male voice. I'll give it a bash on my next trip, can't say I'll be switching to kilometres and metres though, and this may be the root of the problem. Fingers crossed it isn't.

Now, if only it didn't keep crashing every few miles. I nearly picked up a speed camera last night because I hadn't noticed it had frozen on the A30 back from Cornwall...