LONDON— Tesco  PLC aims to turn its vast pool of grocery buyers into bank customers by offering loyalty points and high interest rates on checking accounts, in the biggest effort yet by Britain's largest retailer to shake up the country's tightly held personal-banking market.
Tesco, which sells about 29% of Britain's groceries even after a sharp decline in first-quarter sales, will pay 3% interest on savings of as much as £3,000 ($5,000) and turn account debit cards into loyalty cards that earn points on transactions at the retailer and elsewhere.
The grocer set up Tesco Bank in 1997 for credit cards, loans and savings accounts. Tesco Bank already has six million customers.
A customer passes an advertisement for banking services offered by Tesco Bank. Bloomberg News
Tesco is attempting to turn around its U.K. grocery business, which accounts for nearly 70% of its £70.89 billion in annual sales, but which has struggled in recent years as customers switched to discount stores amid the recession. During that time, Tesco has been criticized for losing focus on its core business by expanding into new areas, including banking, cellphones and even an opticians business. Tesco said last week that its sales, excluding gasoline, in U.K. stores open for more than a year, fell 3.7% in the three months through May compared with a year earlier. Figures from Kantar Worldpanel indicated that the company's share of the U.K. grocery market fell the most in 20 years during the 12 weeks ended May 25.
To win more banking customers, it will have to stand out in a market that is dominated by five banks and includes a clutch of so-called challenger banks that have sprung up in recent years with mixed success. On Monday, TSB Bank PLC, an offshoot of Lloyds Banking Group  PLC, said it would sell shares later this month valuing it at roughly £1.3 billion. Another small bank, OneSavings Bank, listed its shares last week in an effort to expand its mortgage lending.
"Customers have trouble differentiating between one bank and another, and the challenger banks are really varying shades of gray," said Peter Hahn, a lecturer at the Cass Business School in London.
Analysts at Jefferies say challenger banks are in a strong position to take market share from Lloyds Banking Group, Royal Bank of Scotland Group PLC, HSBC Holdings PLC,Barclays  PLC and Santander UK, which collectively control about 80% of U.K. bank deposits and about 70% of loans. Some of the U.K.'s big banks have faced a backlash from customers since the financial crisis, according to Jefferies. Competition authorities have reviewed the market on several occasions but little action has been taken beyond an industry effort last year to make it easier for customers to switch their checking accounts, known as current accounts in Britain. The Competition and Markets Authority is due this summer to say whether it might start a fresh market investigation.
Tesco Bank Chief Executive Benny Higgins said it would be unprofitable on the accounts for at least a few years—presenting a small but additional drag on the broader retail group. But the brand will gain by working its way further into the daily lives of customers, he said. "This is the final brick in the wall," Mr. Higgins said.
Marrying grocery shopping with banking has a checkered history in Britain and elsewhere. Financial problems last year at Co-operative Bank PLC, previously a wholly owned unit of conglomerate Co-operative Group Ltd., weighed on its parent and turned some customers off to the brand. In the U.S., independent banks operating inside Wal-Mart Stores Inc. outlets have been criticized for charging high fees to customers.
Still, reaching customers in stores remains appealing and Barclays has started opening branches in Wal-Mart's Asda supermarkets in the U.K.