A new advertising campaign for Schweppes soft drinks goes one step further than using a celebrity to endorse the product - it uses lookalikes.

The first press advert in the series shows Prince Charles's partner, Camilla Parker Bowles, being fitted for a designer wedding dress. In the second ad, there's a scene in a jail cell with a concerned-looking Margaret Thatcher patting Jeffrey Archer on the hand consolingly.

The most recent ad sees Tony and Cherie Blair looking out the doorway of number 10 towards a gang of reporters. The twist is that Cherie has her hand on Tony's backside - or does she?

The advertisements, which were made by a London agency for the well-known soft-drink brand are so mesmerising that you can't help but do a double take.

It is then that you see that the "celebrities" in the grainy black-and-white shots are in fact lookalikes and just in case there's any doubt, a copy line at the bottom of the ad says "Sch... you know it's not really him/her".

All very well and maybe it would be enough to satisfy the British Advertising Standards Authority (ASA), but it does raise questions over what advertisers can and can't do with a celebrity's image.

In the United States, the estates of film stars such as James Cagney and Marilyn Monroe were quick to realise the power of those actors images even after death.

After several test cases and challenges, the legal system there protects the images of well-known people and their likenesses. Not so in Britain, where it is legal to use someone's image in an ad without their permission - once, of course, they are not defamed by the depiction.

Advertising is a self-regulated industry and under the rules of Britain's ASA (as well as own regulatory body) permission must be sought from the celebrity. However, the code doesn't refer specifically to lookalikes. So, as the Schweppes campaign uses lookalikes, once they can prove to the ASA that the lookalikes don't really look all that alike, then the ads probably don't contravene their codes.