I am scheduled for the Oct. 18th to take the CRT in Orlando. I currently hold a CCNA, CWNA, OSCP, Security+. I have been looking around for study material for the CREST exams and it seems to be non-existent. If anyone else is taking it and are interested in studying please feel free to drop me a pm.
Also for a little background, to be able to touch a .gov systems in the UK you have to be CHECK certified by CESG (guessing it's similiar to NSA here). CREST certs are a requirement to become CHECK certified, so from what I understand CESG helped defined the objectives, etc.
http://www.gchq.gov.uk/about_us/cesg.html <-- Info about CESG
http://www.cesg.gov.uk/products_services/iacs/check/index.shtml <-- Info about CHECK
*Disclaimer* This is just from what I have read and gather from talking to people in the UK