Paddy Power's controversial advert promoting odds on Bladerunner Oscar Pistorius being found not guilty of the murder of his girlfriend is to be withdrawn after it notched up a record number of complaints.

The Advertising Standards Authority (ASA) confirmed it had received an "unprecedented" 5,200 complaints about the ad, which offered punters their money back if the South African athlete were cleared of the murder of Reeva Steenkamp.

The advert, which included a gold Academy Award in the image of the Paralympian, ran with the slogan: "Money back if he walks".

The campaign, featured in British national newspapers, sparked a huge backlash against the Irish betting company. An online petition demanded the "vile and offensive" ad be pulled. To date, the petition has gathered more than 120,000 signatures.

The ASA confirmed it had taken the "unusual" step of asking Paddy Power to withdraw the advert from circulation.

A spokesperson said: "On the back of an unprecedented number of complaints, we are investigating whether the ad is offensive for trivialising the issues surrounding a murder trial, the death of a woman and disability; we are also challenging whether, in doing so, it brings the good reputation of advertising generally into dispute.

"We consider the ad may be seriously prejudicial to the general public on the ground of the likely further serious and/or widespread offence it may cause. We are also concerned that the good reputation of the advertising industry may be further damaged by continued publication of this ad."

The ASA added it would not investigate complaints about the ad appearing on Paddy Power's own website, as the company is based in Ireland and falls outside the UK watchdog's remit.

Initially, the bookmakers refused to drop the campaign.

As the controversy surrounding the advert began to build, a spokesperson for Paddy Power said: "Paddy Power has a long history of offering odds on global news events and the Oscar Pistorius trial is no different.

"Given intense global media interest, including a dedicated 24-hour television channel promising round-the-clock coverage, Paddy Power is giving punters the chance to put their money where their mouth is for what will undoubtedly be the most reported on, and talked about, news story of the year.

"We recognise that there has been some reaction to this market, but we're also listening to the many customers looking to bet on the outcome of the trial."

The record for the most complained about the advert was previously held by KFC. The television campaign, which featured call-centre workers singing and eating with their mouths full of food, received more than 1,600 complaints that it would encourage bad behaviour in children.

Pistorius, 27, denies murdering Steenkamp at their home in Pretoria last February.