3G not working with any "Sat Nav" apps on the iPhone 3G

[Mark]

Today was my first ride into work (30ish miles round trip), I google mapped the route before hand and printed off a list of roads, and landmarks along the way that I'd recognise. All was going well, turn left at McDonalds, carry on then turn right at the blue foot bridge. "errrr.. blue bridge THAT ISNT THERE"
Long story short, I missed it and ended up going down the A6..

My 3G does work. I can get on Safari, Facebook etc, and the satnav apps work on WiFi but for some reason they're not picking up my location on 3G.. Making them totally useless and me ending up being late and burning petrol.

I've tried it on both TomTom and CoPilot Apps.

Any Ideas? :ermm