How do I find person in UK?

[angel]

I want to find my thieving, conniving ex-husband only to get him to pay back the money plus interest he owes me. (I have proof of him owing me money but no redress from divorce as whilst we were divorcing, we had agreed that we would sort the financial details out ourselves... stupid me, I know) anyway, I am sure he is in UK but he is very secretive and I am no longer in contact. He has even closed down his facebook page. I believe I need to know where he is living in order to pursue a civil matter in court. I have looked through various sites on google but would rather not pay online.
Does anyone know of an easy to understand free site? Would love to be able to make some headway of getting back the £50k plus he owes me.

Last time I spoke to him, I threatened to go to a magazine and out him this way, he would hate that so so much (to be seen by new neighbours splashed all over magazine with his private affairs on show) but that would mean MY dirty washing on show too)