LONDON—Tesco, Britain’s biggest retailer, raised its full-year earnings forecast on Wednesday after the unmatched scale of its store and online operations helped it outperform rivals in the first half and deliver a better-than-expected 16.6 percent increase in profit. British retailers are battling supply chain disruptions and labor shortages. Supermarkets also face tough comparisons against record sales during COVID-19 lock-downs. Tesco, however, increased sales in the period. “We’ve had a strong six months; sales and profit have grown ahead of expectations, and we’ve outperformed the market,” said Chief Executive Ken Murphy. “With various different challenges currently affecting the industry, the resilience of our supply chain and the depth of our supplier partnerships has once again been shown to be a key asset.” The group said on Wednesday the strong performance had enabled it to cut net debt by £1.7 billion ($2.3 billion) since February, and so it could afford to buy …