It is Nationwide's first activity since head of sponsorship Peter Gandolfi was promoted to head of brand marketing in August, with a brief to revitalise its £24m marketing strategy.
A series of four television ads will introduce an obnoxious member of staff at a high-street bank, played by comedy actor Mark Benton.
The campaign, created by Leagas Delaney, will position Nationwide as the consumer-friendly choice.
'Because we are a mutual organisation, we do have a point of difference, but the problem is convincing people,' said Gandolfi.
The character will be the lynchpin of Nationwide's future promotional strategy. He will be used in brand advertising and tactical executions highlighting issues such as ATM charges.
The first four executions focus on car insurance, currency exchange, the disparity between deals offered to existing customers and those used to entice new ones, and the problems with one-size-fits-all policies.
'It is a chance for us to deliver an anti-bank message in a less confrontational way,' added Gandolfi. 'We are targeting non-customers to try to predispose them toward Nationwide.'
The initial burst of ads will run from 26 December to 31 March. It will be one of the biggest television campaigns run by Nationwide in recent years. Four further executions are due to be screened from April.
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