As a general rule, where an entity holds 20% or more of the voting power (directly or through subsidiaries) on an investee, it will be presumed the investor has significant influence unless it can be clearly demonstrated that this is not the case. On the other hand, If the holding is less than 20%, the entity will be presumed not to have significant influence unless such influence can be clearly demonstrated.
As per IAS 28, representation on the board of directors is an evidence to the existence of significant influence by an entity. Therefore you can treat your investee as an associate and make accounts accordingly.
