iPhone, iCloud and Mail syncing problem
I don't know the first thing about what the UK Data Protection Act covers, but you can clearly see in the iCloud and Mail, Contacts, Calendars settings that you can slide off Mail yet still slide on the other categories of data.

Contacts (addresses), Calendars, Reminders, Notes.

If it's OK to store that sort of information, then your consultant can continue to use Mobile Me / iCloud to put that information in the cloud. Again, you are trusting them to not store actual "protected data" inside an appointment as an attachment (mail message) as well as not enable the mail slider.

You might just decide to require them to use a hosted mail and account that complies with your data storage requirements. Period, full stop. Sometimes that is the cost of doing business as a professional. 

Also - you can bank fairly certainly that Apple won't change the drop dead date to finish MobileMe since it's been published for about 13 months now.

http://www.apple.com/mobileme/transition.html

All MobileMe mail will shut off on June 30th, 2012 - presumably pacific time in the US.