A High Court judge has spoken of the complications involved in assessing the financial needs of estranged wives who become involved in new relationships while still fighting over money with their husbands.

Mr Justice Mostyn said such relationships were "a significant fly in the ointment" for family court judges asked to decide how much money husbands should give wives following marriage break-ups.

He explained the dilemma in a written ruling on a cash dispute between a journalist and her estranged husband following a family court hearing in Swansea.

The judge, who sits in the Family Division of the High Court, said the husband and wife were both in their 40s.

He said the husband came from a "distinguished" and wealthy Welsh family.

The woman was in a new relationship with a man who was about to buy a house.

He did not identify the estranged couple - or the new man in the woman's life.

"Her relationship has been going on with (the new man) for nine months," said Mr Justice Mostyn, in a written ruling on the case following a family court hearing in Swansea.

"She says she is not going to live with him, although it is perfectly clear that the relationship is strong."

He added: "Relationships like this always are a significant fly in the ointment in the assessment of need.

"One cannot make assumptions, if it is not full-blown cohabitation akin to marriage, that it will grow into that, because if it does not, the wife may be left stranded between Scylla and Charybdis if the assumption is wrongly made.

"On the other hand, if one makes a needs assessment on the basis that she is a single woman and she soon cohabits, then the paying party ... can rightfully feel significantly aggrieved."

The judge reasoned that around £250,000 would be enough to meet the journalist's needs.

"In my judgment, if the wife were assuredly single and I could foresee that continuing, I would have my doubts as to whether a net capital position, excluding pension, which will not be accessed for a long time, of just over £250,000 would be enough," he said.

"On the other hand, I cannot ignore the existence of the relationship ... and so I reach the conclusion that the net figure that I leave the wife with of just over £250,000 is sufficient to meet her needs."