James:
JN is absolutely right about TrueCrypt, it’s an excellent tool. Be aware, however, that you can be compelled to disclose your encryption keys in the UK legally, and you can always be compelled to do so via extra-legal means. If you have any data that you truly wish to keep secret, a good start is to use a second TrueCrypt volume containing important data inside the primary volume which contains
data that is less crucial. Regards, – PH