What could David Beckham do if fakes of his autograph were being sold? The facts behind Victoria Beckham's alleged claim that a Bluewater shop was doing just that are disputed, as shown by the shop's slander claim against her, but celebrities now have better legal protection in the UK against the unauthorised use of their names and images than ever before.

If an allegation that celebrity autographs were fakes were to stand up, disappointed customers could claim misrepresentation, andadvertising regulators and trading standards might get involved. While those laws and regulations are mainly aimed at protecting those buying the autographs, different rights come to the aid of the celebrities themselves.

It was not until March of this year that the English courts categorically held that the unauthorised use of a famous person's image in an advertising context could be objected to on the basis of passing off. This was Formula 1 driver Eddie Irvine's successful case against the talkSPORT radio station over its use of a doctored photograph of him in a mailshot promoting its 1999 coverage of Silverstone. The court found that this prominent use of a celebrity's face was passing talkSPORT off as having been endorsed by Irvine, when in fact he knew nothing about the mailshot.

Irvine's legal victory was bittersweet – he was awarded just £2,000 in damages because of the mailshot's limited circulation (it went to around 1,000 media buyers) and was left with a hefty costs bill. Yet other celebrity "victims" of unauthorised endorsements should be grateful to him for having established a valuable point of principle. While not every single reference to a famous person will amount to passing off, the law has at least been brought into line with modern practices on endorsements.

So why haven't other celebrities fared as well as Irvine when trying to prevent the use of their names and faces? The answer lies in the kind of legal right relied upon, the kind of use and sometimes on the kind of celebrity. The Irvine case hinted that unauthorised baseball caps bearing the Formula 1 driver's image might not have been unlawful. The Spice Girls failed to stop sticker books showing their names and faces in a passing-off case that they brought at the height of their popularity. The Diana, Princess of Wales Memorial Fund resorted unsuccessfully to trade-mark applications in 1999, trying to maximise revenues from its authorised brand merchandise by registering over 50 different photographs for various products. The trade-mark registrations were refused on the basis that Diana, Princess of Wales's image was too well known to operate as a brand.

Trade-mark protection will have to be used more selectively and, strange as it may seem, you stand a better chance of getting a trade mark if you apply when you're nearly famous, rather than waiting until you're really famous. Cannily, the Spice Girls used copyright as part of their armoury: it's said they insisted on owning copyright of photographs of them wherever possible so that they could control their exploitation. Alan Clark had recourse to a lesser-known section of the Copyright Act when suing the Evening Standard in 1998 over its spoof "Alan Clark's Secret Election Diaries". He invoked the little-used moral right against false attribution, as well as the law of passing off, to establish that people reading the Standard with "varying degrees of attention" might not spot the parody and might believe the diaries really were penned by him.

The costs of passing-off litigation make only a small dent in the budget of stars, but there is a cheaper way of objecting to the use of your image in advertising. The codes used by the regulatory watchdogs such as the Advertising Standards Authority, while more focused on protecting those exposed to advertising than the famous who prefer to be paid for appearing in it, deal with the point. It costs nothing to make a complaint: indeed, the ASA tends to discourage the use of lawyers. It was complaints made via this route over the depiction of Tony Blair in the "demon eyes" posters that led to the ASA asking for the ad to be withdrawn.

Advertising lawyers know better than to assume that those regularly lambasted in the press for their policies will also take advertising images lying down. It's hard to predict which celebrities will rise above the use of their name or image, and which will fire off a letter of complaint.

Sarah Byrt is a partner in the intellectual property and IT group of Mayer, Brown, Rowe & Maw