The acting Taoiseach has promised that if necessary emergency legislation to fix laws around suspended sentences will be brought before the Dáil within days.

A raft of test cases are expected before the courts after the High Court ruled yesterday that the 2006 law which allows the instant activation of a suspended sentence was unconstitutional.

The Department of Justice is consulting with the Attorney-General.

Acting Justice Minister Frances Fitzgerald says the consequences and implications of the judgment "have been under urgent examination in consultation with the Attorney-General".

"There are no grounds for believing that persons generally who had not raised this issue in the course of proceedings which have been concluded will now be able to benefit from the finding of the High Court", Ms Fitzgerald said in a statement.

"The government will take all necessary action open to it to address the issues arising from Judge Murray's judgement".

" While legislation cannot retrospectively affect criminal cases before the courts, if, in the light of the consultations with the Attorney-General, it is concluded that amending legislation is necessary, this can be introduced in the Dáil very quickly - if necessary within days".

Enda Kenny says if emergency legislation is needed it will be brought in.

The strike down means prisoners will be entitled to argue unlawful detention in some cases.

The High Court says the instant activation of a suspended sentence when a criminal is found guilty of a second offence is unconstitutional.

Mr Justice Michael Moriarty declared Section 99 of the 2006 Criminal Justice Act as unconstitutional, partly because it allows for significantly different treatment of people before the law, in relation to their rights of appeal.

Striking down the section will affect the criminal justice system from the District Court to the Central Criminal Court.

But solicitor Darragh Robinson of Sheehan & Partners told Newstalk Breakfast the change is unlikely to affect many people.