"The first is that the capacity of a corporation is limited
by its constitution, that is, in the case of a company
incorporated under the Companies Act, by its memorandum and
articles of association; the second is that a corporation
cannot do any act, and that includes making a
representation, except through its agent.
Under the doctrine of ultra vires the limitation of the
capacity of a corporation by its constitution to do
any acts is absolute. This affects the rules as to the
'apparent' authority of an agent of a corporation in two
ways. First, no representation can operate to estop the
corporation from denying the authority of the agent to do
on behalf of the corporation an act which the corporation
is not permitted by its constitution to do itself.
Secondly, since the conferring of actual authority upon an
agent is itself an act of the corporation, the capacity to
do which is regulated by its constitution, the corporation
cannot be estopped from denying that it has conferred
upon a particular agent authority to do acts which by
its constitution, it is incapable of delegating to that
particular agent.
...
The second characteristic of a corporation, namely, that
unlike a natural person it can only make a representation
through an agent, has the consequence that in order to
create an estoppel between the corporation and the
contractor, the representation as to the authority of the
agent which creates his 'apparent' authority must be made
by some person or persons who have 'actual' authority from
the corporation to make the representation. Such 'actual'
authority may be conferred by the constitution of the
corporation itself, as, for example, in the case of a
company, upon the board of directors, or it may be
conferred by those who under its constitution have the
powers of management upon some other person to whom the
constitution permits them to delegate authority to make
representations of this kind. It follows that where the
agent upon whose 'apparent' authority the contractor relies
has no 'actual' authority from the corporation to enter
into a particular kind of contract with the contractor on
behalf of the corporation, the contractor cannot rely upon
the agent's own representation as to his actual authority.
He can rely only upon a representation by a person or
persons who have actual authority to manage or conduct that
part of the business of the corporation to which the
contract relates."