I ought to just say, to head off any extension of the slightly irrelevant discourse above, that no-one I'm dealing with has any issues with this, it's just that it has to be done for specific conversations for regulatory reasons that people are aware of, and I'm trying to cover all the comms channels that we use.
Skype is one element which doesn't fit in well to any of the solutions that we use, and the comms guys that I've talked to have no good solutions beyond Heath-Robinson setups which I know won't work in practice.
If it's not possible then banning Skype is an option - and pretty much a last resort - but I will do it if I have to, so that I'm protected from an unenforceable liability. I'm trying to find a way around that.