Though it is a bit like taking a second job after the house has been repossessed, the Federal Reserve's proposals for new regulations on mortgage lending and advertising deserve support. They will reduce - although never eliminate - the kind of sharp practice that led to this year's subprime debacle. But as well as changing the rules, the authorities need to toughen up their enforcement of them.

The proposed reforms fall into three groups. Group one, targeted at subprime mortgages, would require creditors to check whether a borrower can repay their loan. That may sound as unnecessary as a ban on restaurants selling undercooked food, but in practice it matters: loan sharks were lending with the sole objective of repossessing a borrower's assets long before subprime was invented. The Fed must be careful, however, that its reforms do not prevent the self-employed, who cannot easily prove their income, from borrowing.

The second group of reforms aims to make the fees attached to subprime mortgages fairer and more transparent. Commission paid to a mortgage broker, for example, would have to be disclosed to a consumer in advance. This is fair, although unlikely to make much difference to less financially literate consumers. It is also pointless to make rules that are too specific, as commissions have a slippery ability to mutate in form.

The third group of reforms regards the advertising of subprime mortgages. Lenders would be required to disclose the cost of a mortgage more clearly, including how the cost will rise if it has an introductory discount, as so-called adjustable rate mortgages do.

These reforms are welcome, but do not go far enough. Tempting introductory rates are a widespread and legitimate tactic that bankers use to promote both loans and deposits. In adverts, however, the most prominent interest rate should have to be the one that applies after any introductory bonus expires.

There is a risk that the new regulations produce only box-ticking. A broker, for example, may demand payslips to "prove" that a borrower can afford a loan, but not bother to check whether they have been faked, or whether the borrower has six children, two ex-wives and a gambling habit to support. Given the role of fraud in this year's subprime losses, the risk is serious.

The authorities, therefore, must enforce the rules as well as writing new ones. They must inspect loans at random and send "mystery shoppers" to hear how mortgage brokers explain their products. Where they find abuse, they should prosecute.

There is always a danger of over-regulating after something goes wrong and the point of regulation is not to stop consumers making bad decisions. But the Fed is right to try to make sure that consumers make their bad decisions with full knowledge of the facts.