By the time the House of Lords had finished delivering its double ruling in the Miller and McFarlance cases today, divorce lawyers around the country were already scrambling to interpret its significance.

There was disagreement as to whether it clarified or complicated divorce laws. Many believed it would lead to higher maintenance payments for ex-wives and an increase in pre-nuptial agreements. All agreed on one thing: it was a blow to wealthier spouses.

"Overall it hasn't got better for the husbands," Magnus Mills, a partner at Manches, said. "It's probably slightly better for the wives. White v White [the landmark 2000 case] was the watershed that made things better for wives everywhere and that swing hasn't halted."

Justin Moss, a family law solicitor at Wilsons, a firm in Salisbury, said: "Rich men shouldn't get married, frankly. It's that simple. It's not sensible for anyone, man or woman, to marry anybody financially weaker than they are."

Men or women who are wealthier than their spouse may insist on a pre-nuptial agreement or simply choose to co-habitate rather than marry. Had Mr Miller insisted on the former, lawyers believe, the size of the £5 million award to Mrs Miller would have been substantially smaller. In the latter instance she would likely have received nothing.

"There's no question some people will prefer [co-habitation] because of these cases," William Longrigg, a partner at Charles Russell, said.

Pre-nuptial agreements are currently not recognised under British law, but experts believe that is set to change. "At the moment the courts don't recognise them but many senior judges are already taking the view that the law should accept that adults are more than capable of entering into binding agreements," Mr Longrigg said. "If you enter into a pre-nup you're giving yourself an element of protection even in this country."

Nigel Sheppard, the head of family law at Addleshaw Goddard, added: "The gradual move toward courts giving more weight to prenuptial agreements will be given a further boost by the Miller judgment. I expect to see increased interest in pre-nups from wealthy people in the wake of today."

The law lords' decision to dismiss the consideration of a spouses' conduct in determining a financial settlement was welcomed with relief. Lower courts presiding over the Miller case had ruled that the size of Mrs Miller's award was justified because of her husband's infidelity, but the lords disagreed with that reasoning. Instead, they upheld the award on the basis that £5 million amounted to one-third of the money Mr Miller had made during their brief marriage — one-sixth of his fortune overall.

"Most practitioners still think £5 million was a lot for Mrs Miller to get, but at least here it's justified," Mr Longrigg said. He described the ruling by the lower courts as "very surprising".

Mr Sheppard added: "Family lawyers have long argued that the reasons behind a breakdown should not be considered when working out a financial settlement because the judges do not live with the husband and the wife and the relative faults are never black or white. Arguing over who did what and when is an unwelcome distraction."

Lawyers said the Miller ruling strengthened the precedent set in White v White in 2000, which awarded Pamela White an almost equal share of her husband's £4 million fortune based not on her financial needs, as had traditionally been the case, but on entitlement.

The contribution of both spouses to the marriage should be regarded as equally important, the lords ruled, even if one spouse earns substantially less than the other. In awarding Mrs Miller a large slice of her husband's fortune even though they were married for less than three years, the lords today extended that principle to all marriages, not only long marriages.

The McFarlane ruling, which restored the maintenance provision of £250,000 a year awarded by the original judge to Mrs McFarlane for life, was likely to lead to an increase in maintenance payments demanded by spouses who are financially less well-off, some predicted.

"I would expect to see wives to ask for more, absolutely," Magnus Mills, a partner at Manches, said. "And they'll probably receive more."

Emma Hatley, a family law partner at Withers, the firm that represented Mrs Miller, disagreed that the case had brought greater clarity to divorce laws. "The judgment creates uncertainty and will encourage litigation by those who can afford it," she said.

"There are significant differences in the main judgments of Lord Nicholls and Baroness Hale as to what type of assets would form part of the marital pot for division, regardless of the length of the marriage. Both do seem to accept that assets acquired before marriage and inherited assets are to be treated differently. The decision has made the law less predictable."

Mr Moss said there was already widespread uncertainty over British divorce laws because they depend on an interpretation of what is fair. "There are always going to be different views of what's fair," he said.

"There's no rational formula for fairness. It's an instinctive response, coloured by a judge's social background, his personal life, that sort of thing. They construct an intellectual figleaf to justify their reasoning but it's just gut instinct at the end of the day. It's just one bloke's view. And they usually are blokes."

Mr Moss's advice to people considering divorcing a less financially well-off spouse was: "don't risk it".

He added: "No one in their right mind should fight all the way to trial. There's one certainty in all of this: it's going to be expensive. Do a deal, be generous, and do it early."

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