Thank you it is unlikely he would be able to do this is he is responsible for the underpayment. In addition to this at the time of his retirement, he may be out of time to make a claim for this, it can be quite difficult to change a finical order when one has been made, if he is liable for the mistake he would unlikely be able to claim against you. However if he does do this in time then it would be advisable to have a solicitor assess the merits of their claim. If he sends you a legal letter, you do not have any obligation to do what they are requesting only a court can do this.
I shall provide you with a helpful link that will assist you in finding a solicitor/representative near your local area. This will provide you with someone nearby your area who can assist you if required.
I hope this information proved helpful. You will find a local solicitor who deals with these matters on the law society webpage which is as follows;
https://www.lawsoc-ni.org/solicitors (N. Ireland)
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