In his first public comments since his hostile Senate inquiry appearance, the Woolworths chief executive, Brad Banducci, has delivered worse-than-expected March quarter financial results and admitted the supermarket can “unequivocally improve”. Sales across the group, which includes New Zealand and Big W stores, increased by 2.8% to $16.8bn in the quarter, while its Australian food sales were up 1.5% to $12.6bn. Average prices dropped 0.2%. With the supermarket recording a modest rise in sales, customers were feeling the shock of material increases in mortgages, rent, utilities, insurance and other key household expenses this year, he told reporters on Thursday morning. Sign up for Guardian Australia’s free morning and afternoon email newsletters for your daily news roundup “It was a challenging quarter across the group with a noticeable shift in customer sentiment and shopping behaviours since Christmas,” he said. Investors viewed the results poorly, sending Woolworths shares 4% lower in morning trading compared with a 0.3% increase for the overall market. Overall, the share price has lost about a fifth of its value since the beginning of the year. In April, Banducci was threatened with imprisonment by the Greens senator Nick McKim at a fiery Senate inquiry hearing. He said on...