Luxury car maker Jaguar has been ordered to withdraw an advert which watchdogs said encouraged motorists to break the speed limit.

The advert for the company's XK8 series - headed "suddenly weekends are a blur again" - could encourage "irresponsible" driving, ruled the Advertising Standards Authority.

It is the second time the company has been rapped for using speed to sell its cars.

The advert featured a blurred image of a cornering XK8 above the caption "Ah the excitement, the thrill, the uninhibited freedom of yesterday (Not to mention tomorrow, the day after, the day after that)".

Jaguar said the message conveyed was the pleasure of driving the car which it said was about elegance and refined power.

But an ASA spokesman said: "Jaguar asserted that the average age of an XK8 buyer was 48 and the advertisement conveyed a sense of so much driving enjoyment that weekends would fly by as they did in one's youth.

"They argued that the word blur was right because whatever speed one travelled at the view from the car's side window would be slightly blurred."

He added: "We considered that the blurred wheels and background, together with the tone of the text, unduly focused on driving at speed and concluded that the advertisement could encourage motorists to drive irresponsibly."

Book ad 'not pornographic'

In a separate judgement, the ASA rejected complaints that an advert for books on the internet was "pornographic".

The advertisement for the Bol.com. online bookshop featured a naked man and woman embracing on a bed, each holding a book and appearing to read over the other's shoulder, beneath the caption "Love Books".

The ASA received 315 complaints about the picture, which appeared in a magazine section of a national newspaper and on poster billboards. The complaints alleged it was pornographic, gratuitous, offensive and unsuitable for children.

A spokesman for the ASA said: "The advertisers said their qualitative research showed respondents of all ages thought the visual was witty, light-hearted and a tongue-in-cheek reference to readers' love of books.

"They believed the image was not pornographic or gratuitous but was stylish, artistic and far less offensive than images widely available in other media.

"They said they had instructed their poster contractors to avoid placing the poster near schools and churches.

"We considered that the photograph was unlikely to be seen as pornographic because the couple were clearly reading their books and were not engaged in a sexual act.

"We concluded that although the advert featured nudity, it was unlikely to cause serious or widespread offence."