The UK MoD has certified PGP Corporation's whole disk encryption technology as suitable for use on British military computers. However, like most software-only solutions, it has been approved only for machines holding fairly low-level information.
PGP Whole Disk Encryption had previously passed the UK government's baseline approval process run by the CESG, but has now been certified by the Defence INFOSEC Product Co-operation Group (DIPCOG) forum as approved for use in MoD and military systems. However a disk protected solely by PGP encryption is only allowed to have RESTRICTED (Impact Level 3) information on it.
The British protective markings run from UNCLAS (Impact Level 1-2) to RESTRICTED (Impact Level 3) through CONFIDENTIAL (4), SECRET (5) and TOP SECRET (6).
There are some security products already on the UK market certified to higher levels, for instance Flagstone Enhanced rated for TOP SECRET information - but this requires replacement of a laptop's hard disk with special hardware, which would be overkill for most users. Microsoft's BitLocker, included in some versions of its later operating systems, is (like PGP) only OK'd for RESTRICTED.
But things which in many organisations would be seen as crown jewels - people's personal details, for instance - are classified RESTRICTED in the MoD (albeit usually with an added caveat, eg RESTRICTED STAFF or RESTRICTED MEDICAL, it's still only Level 3). Level 6 is stuff like the planned patrol area of Blighty's nuclear missile submarines.