A formal investigation has been launched into NatWest's MoneySense TV campaign which promotes its free advice service at branches.
The Advertising Standards Authority probe follows the results of a Which? investigation that found the bank's service was sometimes failing on its promise of delivering impartial advice.
NatWest began the MoneySense programme at the end of 2008 with the aim of giving people access to advisers in 1,000 of its branches.
NatWest insists it has done nothing wrong.
Money Box speaks to Which? principal policy adviser Dominic Lindley.