As a charity Trustee your primary duty is to promote the “charitable purposes” of that organisation. These “objects” are set out in either the Articles of Association if the charity is a company or in the “objects clause” of the charity’s governing document.
If a Trustee of a charity allows the charity’s assets to be used for a purpose other than the purpose set out in its “objects” then they will have acted in breach of trust and therefore personally liable for making good any losses to the charity.
Charity Trustees must ensure that the activities of their charity fall within the “charitable purposes” of their charity as set out in the “objects” and should continue to review the “objects” on a regular basis to ensure that the current and proposed activities fall within them. If not then it could be necessary to make changes to the “objects” so that no breach of trust is incurred.