The Ofcom advice linked to above[1] mentions business use specifically.
In short, businesses can only record for some specific purposes (e.g. for regulatory compliance) and they have to adhere to the principles of the data protection act. It particularly mentions some privacy issues with regard to your employees.
I think that the disclosure to other employees would be covered by the DPA guidelines - if it's required for business purposes then it's fine.
[1] http://www.ofcom.org.uk/static/archive/oftel/consumer/advice...
It seems to be standard practice to have a "calls may be recorded for training purposes" disclaimer these days. Some even say "please tell the operator straight away if you do not wish to be recorded".
This doesn't really tell you what's legal or not, but I would assume that the only reason they put that stuff in is because they have to.
For example, could my employees record some calls for each other's use within the business, or would that count as a third party, if those call recordings remained private to the company?