Hi there,
If the address of the Ex partner is unknown, then you can request the court to serve papers using alternate methods, -serving the papers to his workplace or any relatives/friends place , or to serve papers via fax/emails.
Secondly , if you have no contact with any of your Ex's relatives/friends or do not have his/her email /fax, then you can apply to the court for a disclosure order from HMRC.
his order is made against HM Revenue and Customs and you will need to provide your spouse’s date of birth, NI number if you have it and also their last known address.
HMRC will then look through their database and try to find an address for them. If they find an address they will write to the court.
The court will then send the court papers to that address. If they do not respond, the matter goes through without their consent.
Finally, if there is no way of finding your Ex or any relative, then you can apply to the court to dispense with service of the court notice and order Ex-parte (in the absence of the party)