A. You can offer your services to those companies on a self-employed basis, but you need to have a clear contract which distinguishes your work as a consultant from work you do as a director. The self-employed tasks need to be invoiced separately and declared to HMRC as a separate business from your fees as a director.
Generally the fees for work you perform as a director should be taxed under PAYE. Legislation introduced in the Finance Act 2013 requires the IR35 provisions to apply to work done as officers where that work is charged through a third party, such as a personal service company.