Hi Colin,
Unsure of the full answer to this, but I had a similar problem.
My satnav always gave me the warnings, but one day it stopped.
At the time I fiddled with 2 things and it worked, so unsure which one actually fixed it, but you may want to try them both.
1:Was playing around with the voice recognition system
2:Had a previuos satnav location still stored, but didn't delete it on arrival.
Having removed the stored location, and reconfiguring the voice recognition, the speed camera warnings returned.
Hope this helps