CDM Co-ordinator

Whilst I would like to encourage my client to appoint a CDM co-ordinator I would like to establish whether this is mandatory,. The advice under 'client's duties' states that clients must appoint a principal contractor and designer - and that the HSE must be notified (when the project type demands) - but the subject of CDM co-ordinator seems unclear. It seems in the current regulations that the duties have become 'shared' between principal contractor, designer and client. It makes sense to me to appoint an 'unbiased' party to the project - to take on the role of CDM co-ordinator - but I need to be clear about the actual obligations under the CDM regulations. I can give my client a choice - but I do not want to insist that something is mandatory if it is not.