Chief executive Kieron Guilfoyle said many of its users were spending between 750 and 1,000 per year on the 3V cards, implying an overall spending figure in the high single-digit millions. He declined to be more specific on the level of transactions handled by the company, which last week secured 20m in venture capital funding to finance its expansion into other European countries, saying the figure was "commercially sensitive".

Guilfoyle said the company had been surprised by the uptake of 3V cards among people who already own credit cards. One in three of its customers has a credit card but uses the 3V for making purchases over the telephone or online.

The company provides "virtual" credit cards, issuing card numbers and security codes to users who pre-pay a set amount, from a minimum of 20 up to 350 and can then use the number to make purchases, as they would with a normal debit or credit card, up to that amount.

Guilfoyle said the cards are mainly used for online purchases such as travel bookings, concert tickets and transactions with merchants such as Amazon and eBay.

On the back of 3V's successful launch in Ireland the company is planning to expand into Germany, Spain, the Netherlands and the UK.

Last week it announced a 20m investment from Atlas Venture and Benchmark Capital which, Guilfoyle said, will mainly be used to fund marketing as it expands outside Ireland for the first time.