Conflict of Interest
The first issue you need to be aware of is the potential conflict of interest you might create between your duties as a director and your interests as a self-employed contractor. As a director, you have a fiduciary duty to act in the best interests of your company and its shareholders, which means that you should not enter into transactions that are detrimental to the company or that give you an unfair advantage over other shareholders. However, as self-employed contractor, you may have an incentive to charge your company more than the market rate for your services or to provide substandard services that do not meet the company's needs. This could expose you to legal action from the company or other shareholders for breach of fiduciary duty or unfair prejudice.
To avoid any conflict of interest, you should make sure that the terms and conditions of your invoices are fair and reasonable and reflect the market value of your services. You should also document the nature and scope of your services and keep records of the time spent and the expenses incurred. And then you should make sure that you obtain the consent of other company directors as well as other shareholders, if any, before billing your company. You disclose any potential conflicts of interest. Your objective is to prevent HMRC from challenging the validity of your invoices and tax your self-employment income as disguised payments for your work as a director. Which means that you would have to pay income tax and National Insurance contributions (NICs) at higher rates and that your company would have to pay employer's NICs as well.