
The rules [1] for 2013 have been revised by the BGA Council in May 2012. They will apply to the 2013 and all subsequent championships (until amended), and supersede all previous versions, although informally the changes are mostly effective for 2012.
The statement regarding the rules changes is as follows:
In March 2013 Council clarified that if the Champion plays in the Candidates, then he/she cedes their automatic place in the Challengers League.
Links:
[1] http://www.britgo.org/chrules
[2] http://www.britgo.org/taxonomy/term/30