No one plans for a divorce, but sadly, one in three marriages will break down. And not only do you have to cope with the emotional shock of divorce, but there's a dramatic financial one, too.

Who gets the house?

The average price of a house is currently £175,000, a one-bed flat, £115,000. So even if you and your partner sell your house and each buy the cheapest alternative, the pair of you would be an average £55,000 adrift.

Plus, of course, there'd be two lots of council tax, utility bills, repairs etc. And it's a similar story with renting: two flats cost more than one small house. Which all means you are both going to be poorer – and a pre-nuptial contract is unlikely to help: British judges are not bound by them. Nor, legally, do we have any such thing as a common-law wife – so unmarried partners, beware. There’s normally no obligation for your ex-lover to maintain you from now on.

It’s tough for unmarried co-habitees: if you buy out your ex-partner's share of the home, the transaction will be treated as a new purchase and you'll be charged Stamp Duty. Divorcing married couples, though, don't incur this duty – it's treated as part of their divorce settlement. However, whether married or not, when there are children involved, the split is rarely straight down the middle. The law in Britain puts the children's interests first, the courts aiming to ensure that the kids maintain their previous standard of living and hopefully remain in the existing home, at the same school with the same friends.

This usually means that the family home (or a feasible alternative) will be allotted to the parent with whom the children are going to live, regardless of whose name is on the deeds or tenancy agreement and in spite of the fact that this parent may have temporarily moved out when the relationship broke down. With young children, this carer will nearly always be the mother. Generally speaking, only if she doesn't want care and custody or she's a patently bad mother, will Dad get the kids.

There is no longer a “guilty party” in a divorce. The fact that the wife may have slept with half her husband's friends and used his credit card to fund her adulterous hotel bills may make her a bad wife but not, in the courts' view, a bad mother. Blameless or not, both parents have equal financial responsibility for their children – and that's still true even if one partner has no access to the children and/or doesn't even want a divorce.

Frequently, therefore, the father will find himself banished to a poky studio flat, while his wife – and possibly even her lover – lives with his children in the house he paid for. And he will have to cough up maintenance for the children until they reach 17 (or 19 if in full-time education). Only at that far-off stage – providing this was written into the divorce settlement – will the matrimonial property be sold and the proceeds divided between him and his former wife.

So who decides who pays what? Ideally, the divorcees themselves. And once the two of you have come to a conclusion as to what’s fair – for example, Dad pays the mortgage and utility bills; Mum pays for food, clothes and holidays – get a solicitor to draw up a formal agreement.

If you're in any doubt – and even the most amicable divorce can turn bitter – you should engage separate solicitors to represent your interests. Your local Citizens Advice Bureau will help you find one and tell you if you're entitled to Legal Aid.

If after negotiation you still can't agree, you can take your case to court and a judge will reach a decision which is permanently binding – unless circumstances change and one of you goes back to court and successfully appeals.

There are no hard-and-fast rules governing division of marital assets: the court has almost unlimited power to do whatever it sees fit. All assets must be declared for possible division – not just your income and property, but also things like shares, building society accounts, life-assurance policies and cars.

If either of you intends to remarry or live with a new partner, that too must be disclosed, so that the financial implications can be considered (incidentally, alimony for a wife [or husband] ceases if they remarry).

One of you may have capital tied up in a business you run. If so – and particularly if it earns the maintenance money – you're unlikely to be forced to release cash from it if doing so would wreck its viability. Your solicitor would need to find an alternative.

The other big asset you may own is a pension fund. It's usually women who've lost our here in the past, having relied on their men to save for what they thought would be their communal old age. But divorce means they'll get nothing when they reach retirement. Possible solutions are to divide that pension pot with a Pension Sharing Order, give the wife money to fund her own pension, or for the man to split his retirement lump sum when the time comes.

If you've relied on your husband's National Insurance contributions to pay for your State Pension, remember only the years you were married will count. After that, you’ll have to fund your own pension – your local Job Centre will help you clarify your position.

In the turmoil of divorce, it's easy to forget other matters that need attention: closing joint accounts and re-opening them in your name alone, contacting utilities to tell them who to bill, informing your Tax Office, writing a new will... and, if at all possible, taking out an assurance policy to protect your children financially should you die or become incapacitated, and one on your ex-husband/partner for the same reason.

And all this shows that, while two can live as cheaply as one, the moment you divorce, you're in a whole different world...

Recent developments

Back in May, the Law Lords ruled on the settlements awarded in two high-profile British divorce cases – McFarlane’s and Miller’s – and the decisions they reached have implications for everyone.

Previously, a maintenance figure was arrived at on the basis of need, but their Lordships felt it should be evaluated on what is fair, treating each spouse equally, whether they were wage-earner or home-maker, and compensating one partner for having given up their own career earnings. If there was enough income to do more than cater for basic needs, the wife (or husband) should share the surplus.
Hence they awarded £250,000 of Kenneth McFarlane’s £750,000 annual income to his ex, who’d given up her own successful law career to support him and bring up their three children during an 18-year marriage. And, because this equal sharing of assets should apply as much to short marriages as long ones, they awarded Alan Miller’s ex-wife, formerly also a high earner, £5 million of his £17.5 million fortune, even though the marriage had lasted under three years.

Child-maintenance payments

If one of you is going to claim state benefits (other than Child Benefit, Working Tax Credit or Child Tax Credit), the job of calculating the amount due and collecting it falls to the Child Support Agency (CSA).

• A non-resident parent earning between £200 and £2,000 a week must pay 15 percent of their net income for one child, 20 percent for two children and 25 percent for three or more children.
• There are reduced rates for anyone earning less than £200 a week. So, a man earning £24,400 a year (after deductions) with two kids living with their mum would pay maintenance of £94 a week. That would go down to £81 if the children spend a couple of nights a week with him. It’d go down still further, to £68, if he has a child to support by a new relationship. Moreover, it would probably be even less if he was paying the children's boarding-school fees, the mortgage on his ex's home or some debt the couple took on while still together.