M&S has decided to abandon the charge it had introduced for bras sized DD and above, which it argued was due to the extra handiwork needed to make them.
It has taken out national press ads to publicise its decision and is also offering 25% off all bras for the next two weeks from tomorrow.
The retailer, which is one of the biggest sellers of underwear in the UK, had originally said the charge was justified because larger bras need more work to provide the extra lift.
However the decision, which was described by some as a "tax on big boobs", was not supported by consumers.
Today both The Sun and the Daily Mail are claiming credit for the u-turn. The Daily Mail also credited the online campaign Busts 4 Justice, whose Facebook group has attracted 8,000 members.
M&S chief executive Sir Stuart Rose was clear that The Sun had helped swing it.
Speaking exclusivley to the tabloid, Rose said: "We always try to do the right thing by our customers and we thought we had. But as The Sun has shown it's clear we've got it wrong this time."
This is not the first time M&S and Rose have come under fire for their underwear policy. Last year Newsnight presenter Jeremy Paxman fired off an angry email to the retailer stating the quality and longevity of its smalls had declined.
Paxman later said about the leaked email: "Nothing I have ever done -- interviewing Michael Howard, asking Tony Blair whether he prays with George Bush, nothing -- has elicited such a response.
"I have been deluged with emails; strangers have accosted me in the street saying, 'Good on you'. There is a real issue here."
In response, Rose defended the store's underwear, which is worn by one in five UK men, and invited the presenter to have his pants tested by M&S technical experts.