Tesco, which is Britain's biggest retailer, said the first two Jack's stores open Thursday followed by up to another 13 over the next six months.
Jack's is named after Jack Cohen, who in 1919 founded the business that became Tesco, and is a significant move by Lewis, who has rebuilt Tesco after a 2014 accounting scandal capped a dramatic downturn in trading.
"The intention is for us to be cheapest in town", he said at the Chatteris store, which was built as a Tesco supermarket but was mothballed in 2015 when the group was in crisis.
Tesco now offers over 25,000 products but Jack's will only offer 2,600 products including Jack's own brand items as well as big brands such as Coca Cola, Cadbury's and Lea & Perrins.
Tesco said that eight out of 10 Jack's food and drink products will be "grown, reared or made" in Britain.
The store will have an own-brand range as well as other grocery brands, and like other discounters, will stock homewares on a "when it's gone, it's gone" basis.
To compete with them, Jack's would have to expand rapidly while undercutting Aldi and Lidl's prices at a time when the two incumbent discounters are bound to review their own costs in a bid to show the new kid on the block who rules this roost.
Over the next six months Tesco will launch between ten and 15 Jack's stores in the United Kingdom, with a mix of entirely new sites, sites adjacent to existing Tesco stores, and a small number of converted Tesco stores. They have lowered prices and improved service, but analysts say that with Aldi and Lidl growing at 10% a year it makes sense for Tesco to try to capture some of that growth.
He said he usually shops at Tesco, Lidl and occasionally Waitrose, but added if he had a local Jack's store "I think it would influence me to go and buy some things".
The flag-waving also lets Tesco contrast its United Kingdom roots with the German ownership of Lidl and Aldi, at a time when Brexit has heightened some Britons' awareness of nationality.