Hello, my name is XXXXX XXXXX it is my pleasure to assist you with your question today. When was the money given to you exactly and have you either repaid any of it or acknowledged you owe it since then?
Whatever the reason for the money, even if it was intended as a loan, he will be out of time to pursue this as a claim now. Any claim under contract, which this would be, even if no written contract existed, has a statutory time limit of 6 years to be pursued in the courts. If the money was given to you 16 years ago then he is way out of time to be able to make a claim for this in the courts now.
There is one small loophole in that if the debt has been acknowledged or a payment made towards it at any point, then the time limit to claim would start to run from that point but as long as you have not made any repayments towards it or made any formal acknowledgment that you owe him anything, he would be out of time and even if he tries to make a claim, you can get it struck out for being out of time.
At this stage, you can simply inform him that you do not acknowledge you owe him anything and that he should not contact you any more about this as he is out of time under the Limitation Act 1980 to bring in a claim for this.
Hello, I see you have accessed and read my answer to your query. Please let me know if this has answered your original question or if you need me to clarify anything else for you in relation to this?
The tax office (HMRC) would be your first stop for that - they should have your working history