The Government will have to draw up new legislation to complete the M50 motorway at Carrickmines after the High Court ruled it has acted beyond its powers.
The court overturned Government orders of 1996 and 2002 which changed the system allowing for work which could destroy national monuments.
Mr Justice Nicholas Kearns also quashed consent given by Minister Martin Cullen last year for demolition work on the medieval Carrickmines Castle.
Dún Laoghaire /Rathdown council has given an undertaking not to carry out any work which would adversely effect the monument pending new legislation.
However, other work on the motorway will continue.
