The Law Department principal Justin Selig, who is leading the case, received a “very positive” response from a barrister consulted after the lawsuit was suggested.

He said: “It looks like the bank’s actions are open to challenge on a number of different fronts. What we need to do is work out how we are going to do it and get as many people involved as possible.”

There were a couple of different approaches the landlords could take, he said. In particular, there was the question of whether claimants should pay the increased rate when it begins next month.

Selig encouraged other landlords hit by the rate rise to contact him if they wanted to join the class action: “The Bank of Ireland is going to be using all the big legal firms. But I am not worried about that because we have got a good case and we have good people – we will bring in expert support.”

Landlords began planning a class action after the Bank of Ireland announced it would be doubling rates on certain tracker mortgages earlier this year.

Those hit included mortgage broker Caroline Grierson, who said she felt ‘cheated’ and questioned the need for rates to rise by such a large amount.

A coalition of landlord representatives decided to challenge the decision on the basis that even if the small print allowed for a rate increase, the move was inherently unfair.