Regulation 43:(1) Any person other than the registered proprietor alleging interest in a registered trade mark in which an application is made under regulation 42 may apply to the Registrar in writing for leave to intervene, stating the nature of his interest, and the Registrar may refuse or grant such leave, after hearing (if so required) the parties concerned, upon such conditions and terms as he may deem fit.(2) Before dealing in any way with the application for leave to intervene the Registrar may require the applicant to give an undertaking to pay such cost as in the circumstances he may award to any party.