The company, which has more than 14 million active customers, said on Tuesday that full-year retail sales would rise by between 30 and 35 percent, up from its previous 25-30 percent guidance.
It reported retail sales of 889.2 million pounds for the six months to end-February, beating consensus of 879 million pounds.
Pretax profit rose 14 percent on 27.3 million pounds on total group revenue of 911.5 million pounds.