Following the high profile news of an ex-Foxtons employee being sued on claims that they 'stole' large amounts of valuable property, vendor, landlord and tenancy information, data security is one of the hot topics of the moment.
While you can limit access to information for junior roles who do not require it, a senior staff member needs more freedom to be able to do their job to the best of their ability. So, non-compete contract clauses aside, you will need to work on a trust basis to some extent.
However, as Global Edge points out, there is something that every business can do to protect themselves at little or no cost. Occasionally including a couple of honey trap phone numbers and email addresses in your database is a good idea.
That way if the information should ever be mis-used, at least you will be alerted to it and have some evidence to support any claim.
The manager would be sure to notice if a new Landlord suddenly appeared on the database from nowhere.
From what I understand non-compete clauses are virtually impossible to enforce so it really is down to trust.
Non-compete clauses are legally binding - but that does mean you have to be willing to sue to enforce. Not exactly a recommended route!
Martin
This seems more like a problem under the Data Protection Act (Always important to keep any data you hold encrypted) but then you are relying on the clients to complain.