The John Lewis Partnership retail group has said trading on the High Street is tough but sales are growing.
The firm, which operates department stores and Waitrose supermarkets, said sales grew 1% and 4% respectively in the six months to 30 July amid "extremely challenging" conditions.
Half year profits fell 18% to £90.4m, hit by increased investment and its "never knowingly undersold" commitment.
John Lewis Partnership said it had created a net 1,100 new jobs.
The company's chairman, Charlie Mayfield, said the company's price pledge was squeezing profits as rivals discounted sharply and it was forced to match them, but he said the promise was vital to the company's success.
He told the BBC: "Absolutely it's costing us money, but it is really important we stick to it."
Investment for the six months to the end of July rose by £99m from the same period last year to £254m on new systems, including expanding its own Waitrose delivery service, and improvements to the website.
Waitrose invested £15m alone upgrading its flagship store in Canary Wharf, east London, and John Lewis invested £35m in its 33rd department store - also in east London - at Stratford, opposite the 2012 Olympic site.
Mr Mayfield defended the investments, saying the business was there for the long term: "We expected our profits to be down in the first half because we are investing now, not just for this year, but for the next 10 or 20 years."
"We've done this before and it really paid dividends."
The Partnership is owned by its 76,500 staff, who receive a share of any profits at the end of the company's financial year.