Total sales, including new stores, were up 2% compared with 2.5% in July last year, while the three-month rolling average shows growth of like-for-like non-food sales outpacing food sales for the first time.
So-called big-ticket items such as furniture and household appliances continue to struggle to sell with growth being promotion-driven.
Online, mail-order and phone sales of non-food items show stronger growth, up 15.6% against growth of 9.6% last year.
More top news
The expansion of the probe came as Jeremy Corbyn declared Carillion's demise a "watershed moment" that should end "rip-off privatisation".
Cold with clear skies coupled with rain, sleet & snow
Danish inventor Peter Madsen has been charged with murdering Swedish journalist Kim Wall during a trip on his private submarine.