Just a quick review for this, because sometimes these things are beautifully simple.
Gridpoint GB is an app for the iPhone, available from Apple Store, which very simply displays your current location as an Ordnance Survey 10-digit grid reference.
Because the iPhone has a built-in GPS, it can do this even when there is no phone signal.
The app displays your location with a potential accuracy of 1 metre, and then underneath tells you clearly how confident it is in that location as a +/- accuracy.
And since not everyone is able to relate an OS grid reference to a map, the blue diagram shows your position within a given square on the OS map so you can quickly pinpoint yourself visually.
The advantage this app has over the iPhone’s own Compass app, which displays your location in non-OS grid reference (Eastings and Northings) is that you don’t need any kind of secondary convertion.
There’s more information on the developer’s website – MacKerron.com.
More: Apple App Store
With thanks to Daniel at TGO Magazine for the heads-up on this