FCB Inferno created the ad, which is called "get Christmas all wrapped up", and talks about The Post Office’s longer opening hours and discounts in a bid to get more people using the service over the festive season.
The ad opens in a Post Office, with a flamboyantly dressed Webb – playing the minister of Christmas – and his dachshund helper. Webb light-heartedly describes how the Post Office can help people over Christmas and is joined by Lott who arrives in the Post Office to send presents.
Jim Carter, an actor in Downton Abbey, also makes a brief appearance in the ad.
The TV campaign, which first airs on The X Factor on ITV tonight, will be backed by retail, digital and social executions.
The work was written by Ali Dickinson, art directed by Jack Walker and directed by David Kerr through Hotspur and Argyle.
Peter Markey, the chief marketing officer at the Post Office, said: "Christmas is our busiest time of year with millions of people visiting our branches to post Christmas gifts and of course collect and return online shopping.
"We’ve been working hard to make things easier for our customers this year. With over 3000 branches open for longer than ever this Christmas it’s the perfect time of year to tell everyone about the great changes that we have made.
"I am thrilled with the creative offering that FCB Inferno has brought to the table. It is engaging, funny and undeniably Christmassy."
The Post Office is reviewing its creative advertising account in a process managed by Red Salt.
The agencies remaining in the pitch include DLKW Lowe, WCRS and Ogilvy & Mather. Dare is the Post Office’s incumbent agency but was not invited to re-pitch because it is not one of the Government's roster agencies.
FCB Inferno was brought on board, without a pitch, specifically to create the Christmas campaign.