Single credit card debts becoming joint debts ??

During our marriage STBX and I have always had credit cards in our own names. I used mine for my own spending and spending for items for the home (holidays, furniture, furnishings). I always cleared mine.

During mediation (and despite me asking continually during the marriage and STBX refusing point blank to tell me), he''s declared double digit thousands of pounds of debt on his own cards - news to me. The reasons were dubious and sounded personal though he threw joint spending into the ring (which I vehemently disagree with)

Can these be taken into account as joint debts ?

One of the solicitors I spoke with said that credit cards (cc) in your own name are not deemed marital assets/liabilities..yet the mediator noted them down as such

Can he throw his unsecured cc personal debts into the ring in order to get some of my assets/savings ?