The group, which operates the Blacks and Millets chains, said its outdoor business had performed "broadly" in line with expectations during the period, with like-for-like sales down 5.2%.

But boardwear "continued to be very difficult", with same store sales down 16.1%. That dragged group sales down 7.7% overall in the six months to August 30, a deterioration from the 5.4% drop seen during the first 19 weeks.

Blacks said trading in the first few weeks of the second half had been more encouraging.

"The full year performance will, as ever, depend upon the important fourth quarter trading period," it added.

The group's first half losses before one-off items last year were £600,000, and chief executive Neil Gillis has been trying to launch a turnaround including a store refurbishment programme and head office cuts.

Blacks operates 260 Millets stores, 110 Blacks stores and 57 Freespirit and O'Neill outlets. Shares fell 12% after the warning.

Blacks Leisure said recently its outdoor arm benefited from a boost in camping popularity over the summer. Sales were up more than 6% in July and August, it said.

The group added it is making good progress in securing cost savings in the business, with £5.6m already delivered so far.

Chief executive Neil Gillis said in July that about 100 out of 350 jobs had gone at head office, with a surfwear warehouse also closed in Washington, Tyne & Wear.