Its an old one!
Regulation 87 of the Road Traffic (Construction, Equipment and Use of Vehicles) Regulations, 1963
The electronic Irish Statute Book (eISB) comprises the Acts of the Oireachtas (Parliament), Statutory Instruments, Legislation Directory, Constitution and a limited number of pre-1922 Acts.
www.irishstatutebook.ie
87. (1) Where a vehicle as allowed to remain stationary on a public road, the driver shall not, subject to sub-article (2) of this article, leave the vehicle unattended unless—
(a) the engine of the vehicle is not running,
(b) where the engine is contained in a separate portion of the vehicle capable of being closed, such portion is closed, and
(c) where the vehicle is fitted under article 31 of these Regulations with a door or doors capable of being locked or with a device for preventing unauthorised driving, such door, doors or device is or are locked so as to prevent the vehicle being driven, and, where appropriate, the key of the door, doors or device is removed from the vehicle.
(2) Sub-article (1) of this article shall not apply to a fire brigade vehicle, the engine of which is being used for any fire fighting or rescue purpose.
(3) Where a vehicle which is required to have a parking brake or a braking device capable of acting as such is allowed to remain stationary on a public road, the vehicle shall not be left unattended unless that brake or braking device is effectually set:
Provided that this sub-article shall not apply where the driver is requested by a member of the Garda Síochána or a parking attendant (licensed or authorised as such under the Act not to set the brake.