Latest figures show like-for-like fashion sales were down 1.2% year on year for the week to 5 May.
In-store sales were down 2.6% as retailers fought against declining footfall.
The BDO high street sales tracker also showed shopper numbers fell by 5.7% week on week on the high street and by 3.1% at shopping centres, but footfall to retail parks was up 0.4%.
There was a 0.9% increase in total like-for-like sales across all sectors.
Total in-store sales were down 0.7% year on year, but there was a 10.2% increase in non-store purchases.
Both homeware and lifestyle registered an increase in total like-for-like sales, up 5.1% and 5.4% respectively.