The Derby internet bank Egg has plunged into the red because of losses in its French business.
But it has seen a major increase in consumer borrowing at home.
Egg made pre-tax losses of £22 .8m in the six months to the end of June, compared with profits of £1.2 m a year ago.
But the losses were almost entirely due to its French business - profits in the UK operation more than tripled to £36 .7m.
In the UK its unsecured lending balance which includes both credit cards and personal loans, grew by £650m.
Customers put more money onto their credit cards, and the total amount drawn down as personal loans was almost three times higher than the same period last year.