There seems to be a rather mixed news story written recently on Crown Copyright and CC-BY compatibility:

http://www.iwr.co.uk/information-world-review/news/2259098/crown- copyright-switches

8 March 2010

'Crown Copyright switches to Creative Commons

It will be replaced by a Creative Commons type licence, devised by the Office of Public Sector Information (OPSI), which is already used on data.gov.uk. Jo Ellis of OPSI said: "We have drafted a simple and enabling set of terms and conditions for the site which means that data available through data.gov.uk will be re-usable both commercially and non-commercially. These terms and conditions have been aligned to be interoperable with any Creative Commons Attribution 3.0 Licence."'

The story doesn't seem to go into much detail, so it's unclear whether this is just for data.gov.uk or not... If it is true, then it sounds like incredibly good news, both in general and also for the Wikimedia projects.

Mike