Whatever happened to...
The BNC used to be made available with a programme called Xaira. You can still get this from the Xaira homepage, but it isn't supported any more.
There used to be a simple search box on the BNC home page on this website, which sent a query to a server hosted at the British Library and returned some examples of a word or phrase. This service depended on software which is no longer supported, and could not be updated to work with the latest and very necessary security configuration on the server, so the service was withdrawn at the end of 2015 .
The service offering copies of the BNC with the Xaira software on optical disks was withdrawn at the end of 2013. See more on Martin Wynne's blog.