Intervention by third parties
80.—(1)  Any person other than the registered proprietor alleging interest in a registered trade mark in respect of which an application is made under rule 78 may apply to the Registrar on Form T.M. 29 for leave to intervene stating thereon the nature of his interest, and the Registrar may, after hearing the parties concerned if so required, refuse or grant such leave upon such terms and conditions as he may think 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 costs as he may award to any party.