FNB recently launched a newspaper advertising campaign which includes claims that it is the only South African bank to offer free online, mobile and telephone banking.

On Thursday, Standard Bank used its Twitter account to reveal: "We instruct attorneys to lodge complaint with ASA against FNB for advertising that misleads the public," adding: "FNB ads mislead South Africans by laying claim to several firsts."

The bank expanded on the move in a blog post, quoting Peter Schlebusch, chief executive, personal and business banking: "Customers have the right to know the true facts. FNB's advertising is clearly misleading and factually inaccurate; and should be withdrawn."

News of the complaint, and the way it was made public, drew a mixed response, with most Tweeters taking FNB's side against its "whinging" rival, a fact picked up by FNB CEO Michael Jordaan, who fanned the flames by posting: "Customers responding on Twitter to competitor's complaint against FNB. Go check it out."

Standard Bank fared no better on its blog, where comments were overwhelmingly negative, typified by one headlined "Waaahh Waaahh Dry your eyes".

The following day saw the appearance of a new blog post, entitled "Social media shows its clout," in which the bank insisted that its complaint is valid but implicitly acknowledged its PR failure.

"At Standard Bank we are encouraged, but not surprised, to see how passionately the social media community has responded to our impending complaint to the ASA (Advertising Standard Authority).

"The announcement was made in social media because we value our online communities and felt that they should hear it first hand from us. We respect our community's views and value the transparent relationship we share with them," says the post.