The ad was created by FCB Inferno and is called "unexpected places". It first airs on UK TV on 1 February, when the Post Office will also announce that it aims to become one of the country’s top five financial services providers by 2020.
Webb, who first appeared in the Post Office’s Christmas campaign in November 2014, returns as the organisation’s hyperactive and check-suited "minister", accompanied by a similarly attired dachshund.
Webb drops into people’s beds, and emerges from couches as he explains what products Post Office Money has to offer.
The TV spot will be supported by digital out-of-home executions across London, as well as social media activity.
Pete Markey, the Post Office’s chief marketing officer, said: "The launch of the Post Office Money sub brand is a very exciting step forward bringing great value products together for the first time through a brand that customers can trust.
"The new campaign reflects this by taking the customer on a journey of what the Post Office really has to offer."
The work was written by Jack Walker, art directed by Ali Dickinson and directed by David Kerr through Hotspur and Argyle.