Gordon Brown is idiosyncratic when it comes to talking about money. He always adds a spurious “s”. Instead of saying, “I have saved £3 billion by cutting out free coffee at the Treasury”, he says, “I have saved £3 billions”. As that extra “s” slides through his teeth, it almost sounds like a challenge: “£3 billionsss, count them!”

But I wonder if he will be quite so keen to add his extra “s” when talking about the billions that HM Revenue & Customs has flushed away since the implementation of tax credits in 2003. A report out this week by an influential group of MPs lambasts the inept handling of an awful system, The first problem with tax credits is that they are not one straightforward payment. There are two types of tax credit, all with myriad elements, including the family element, the child element and the family element with baby addition. Confused yet? I hope not, because now the real fun starts.

Once you have navigated the maze of applying for the payments, you must then tell the Revenue if your circumstances change – if you start a new, better-paid job, for example – so that your payments can be adjusted accordingly. But in many cases the Revenue was unable to recalculate the new payments correctly. The calculations are so fiendish that recipients could not hope to hazard a guess at how much they should be receiving and relied on the Revenue to tell them what was what.

Many readers have contacted us to tell us how they tried to do the right thing by informing the Revenue about their new circumstances. Some had even called the Revenue to say that they thought they were receiving too much money. They were reassured that they were not, only to be contacted months later with demands for repayments, leaving them in financial strife.

The Revenue also lost money because of straightforward fraud by conmen pretending to be eligible recipients. Sometimes there is the insinuation that those who mistakenly received overpayments were fraudulent, too.

The vast majority were not, and Mr Brown should make this crystal clear the next time he talks about the “billionsss” paid out in tax credits.

Young couples must remove their rose-tinted glasses

You don’t have to look far to see how messy money becomes when love goes out the window. High-profile divorces – Sir Paul and Lady McCartney; Karen and Ray Parlour, the former Arsenal footballer – remind us that marriage and romance can turn into mistrust and recrimination. But a noncelebrity couple’s break-up has moved the goalposts for couples who thought that they could avoid a messy financial split by not getting hitched.

Derha Dowden and Barry Stack have never graced the cover of Hello! magazine but, as we explain on pages 10-11, a recent decision by the House of Lords over the division of their assets, when they split up after 27 years living together, should grab everyone’s attention. The ruling spells out that unmarried couples should call in the lawyers and sign a prenuptial agrement before they move in together if they want to ensure that they leave a failed relationship on the same financial footing as they entered it.

Under current rules, divorce courts can poke around in a married couple’s history together and use its discretion to decide how to split their assets. Unmarried couples who cannot agree on who gets what can also go to court, but the judge has little power to decide how the assets are divided. It does not matter if one partner paid the mortgage and put down a hefty deposit – if the house is in both names, it will, in all but the most “unusual” cases, be split equally between partners.

Ironically, a “prenup” for unmarried couples holds more sway in court than a similar agreement signed by married couples, precisely because the judge has less room for discretion in the former case.

But if you plan to move in together, how on earth do you raise the issue of signing such a document? Over a romantic dinner? In the middle of a plate-hurling argument? Well, Times Money can help. Experts have recently been bemoaning that too few young couples make a will. If you own property, this is a good idea. And while you are in the solicitor’s office, you can raise the subject. I’ll leave the precise wording to you.

Put your best foot forward to combat rising interest rates

Hindsight is a borrower’s worst enemy. In hindsight, homeowners on variable-rate mortgages will reflect that they should have switched to a fixed-rate deal before Thursday’s rate rise. In hindsight, borrowers locked in to fixed rates may think that they should have opted for five years rather than two.

But borrowers berating themselves about their lack of action before Thursday should not panic. Many lenders started to price in this latest increase weeks ago, withdrawing their low-rate deals to replace them with more expensive loans.

In fact, only those who switched their mortgage deal in the days after the Governor of the Bank of England wrote his letter to the Treasury to explain why the March inflation figures had busted through the 3 per cent ceiling last month would have managed to clinch a fixed-rate deal that was not already charging them for the rise in rates.

Forget hindsight, the important thing is to take action now to protect your wallet as much as you can. Turn to page 8 to find out how.