At least 100 orders for possession of homes sought by lenders since December 2009, could be struck out following a judgment by the High Court.
That is according to the group New Beginning, a group of lawyers, and business people set up to represent and defend mortgage holders.
Hundreds of other people who are in arrears with mortgages created before December 2009 could also be affected by the decision. NewBeginning says it puts a question mark over the entire repossession system since 2009.
The High Court ruled today - on July 25 - that a lending institution cannot apply for an order for possession where a mortgage was created before December 1, 2009 but a demand for full payment was not made until after that.
Ms Justice Elizabeth Dunne was giving her decision in four cases taken by lawyers linked to the New Beginning group.
The decision arises due to the repeal of 1964 legislation by the Land and Conveyancing Reform Act of 2009.
The 2009 Act came into force on December 1, 2009 and only covers mortgages taken out since then.
Ms Justice Dunne ruled that a lender can apply for an order under the old legislation only if they made a demand for the principal monies due before December 2009.
She struck out a case in which that had not happened.
She said the repeal of the old legislation had created a "lacuna" and it was not for the court to supply that which was not in the 2009 Act.
NewBeginning say they have around 100 cases on their books where demand was not made until after December 2009.
A spokesman for the group, David Hall, said the judgment meant there was a significant question mark over the entire repossession system since December 2009. He said we were now in uncharted waters.
It is possible for lenders to seek repayment of the monies due on a mortgage by looking for a judgment order against a person and then converting it into a judgment mortgage. But that is a lengthier and more complex system according to some legal sources.