Wow, a rare example of government doing the right thing, and getting it. Recently the Ordnance Survey opened up most of their map data. I wrote off for a small selection of maps (they send it to you on super-flexy eco-DVDs) and yesterday they arrived.
What I got was (I think) the whole of England at OS StreetView level, and some other disks of location data (name to map location mappings and so on). The format is really open — TIFF for the maps, and CSV files for most of the other data. Full marks to the OS for releasing this under a CC-compatible license.
I’m still exploring it, but here’s a random snippet of StreetView of Bedford so you can see the level of detail:
Richard WM Jones 
TIFF is not open data, it is a raster map in a high-quality image format. Truly open data comes in shape files (for ArcGIS) or KML.
Fair point. I believe that the underlying “construction” data will be made available too, but please check the OS OpenData site for the details.
Edit to add that the disks contain a lot of non-picture data too which I’m still studying, and these disks are only a tiny fraction of the entire dataset that was released.
Hi Rich, I work at Ordnance Survey and it’s great to hear such a positive reaction to OS OpenData. What are you planning on doing with the data? Let me know because we’d like to showcase the best uses on our blog after the election – http://blog.ordnancesurvey.co.uk/
Paul, excellent work.
At the moment, I’m just advocating it and I don’t have any specific plans. I’ve asked Fedora to clarify that the license is compatible with Fedora (I’m sure it is, but they need to go through the legal wheels), and once that has happened the data should be free to be used in all sorts of cunning Fedora & Linux programs, (subject to the license naturally).
One thing that seems like a no-brainer is that the OpenStreetMap folks will integrate all the data into their project, which seems like a massive win.