The campaign, which will run for six weeks from next week, consists of four ads, each focusing on a different Hovis loaf Soft White, Wholemeal, Best of Both or Granary.
The ads depict a different person making a sandwich before cutting it into eight pieces to create a Union Jack shape.
Interest in British-sourced food and drink had been heightened by Kraft's acquisition of Cadbury, said Hovis boss Jon Goldstone.
"There is definitely a consumer appetite for British-sourced products as they feel the injustice of Cadbury's sale to the Yanks," he said. "People are outraged. Hovis is an iconic British brand and it feels like too few British brands are owned by British companies."
Goldstone admitted that the £30m Go On Lad advert, which ITV last week named TV ad of the decade, would be a hard act to follow.
He called on Warburtons and Kingsmill to help drive growth in the category. "Naturally, I hope this campaign will help us take share from them," he said. "But all three of us have an obligation to get the market into long-term growth."
The campaign will be supported by a heavyweight poster push. The first Hovis products to be made just with British wheat rolled out to retailers this week.
Switching to 100% domestic wheat supply had required a "massive multimillion pound investment" spanning five years, said Goldstone.