According to the [OpenData licence][1], all data can be safely assumed to be under a [CC-by 3.0 license][3] - the T&C Explicitly say so:

> ### Creative Commons
>These terms have been aligned to be interoperable with any Creative Commons Attribution 3.0 Licence. This means that you may mix the information with Creative Commons licensed content to create a derivative work that can be distributed under any Creative Commons Attribution 3.0 Licence.

If you want to use outside of that licence, then speak to a lawyer, or read over the licence yourself

 [1]: http://www.ordnancesurvey.co.uk/oswebsite/opendata/licence/docs/licence.pdf
 [3]: http://www.ordnancesurvey.co.uk/oswebsite/opendata/licence/docs/licence.pdf