I expect that many undertake this multi role situation on a regular basis you must be a character that does not easily get bullied/waylaid etc by anybody and you must be able to balance the different roles and be confident as well as competent in what you are doing in both areas

I've not done so myself but have had a lot of experience with CDM-Cs as a principal contractor and now act as one myself. It will take a good strength of character to separate the rolls and not allow oneself to be bullied either by the employer or the designers etc. Being both rolls should mean that there are adequate resources in time and money to do do the job properly if allowed to do so. The CDM-C will need a firm committment from the employer (client) that the CDM-C's roll will be treated with all seriousnes and not just as lip service to the roll. I would suggest if you are taking the roll you separate the jobs and make sure all advice etc is in writing and keep records. The CDM-C has legal duties and could be prosecuted separately if the "cleint" tries to use the defence that the CDM-C hadn't advised properly. There is also the question of competenct to do the roll as in appendix 4 of the CDM regs. With the right planing and commitments there isn't any reason that this won't work though.

Yes but been in the more fortunate role of being a contractor so slightly detached from the client side. The upside is that an in house resource should have a very clear idea of the clients interests and how things work with the organisations. The downside is clearly that even in the best run businesses the CDM C will face pressures if their is a conflict where they are challenging what the client side is wanting to do. Clearly the ideal is to have an in house resource that is very independent and has strong characters who can resist the pressure and ensure that the CDM C role is delivered to the best standards and in line with the legislation. These persons will have good local expertise of the firm and can react quickly in the event changes of priorities.