The service was knocked offline when an attempt to upgrade it went wrong. It is now running normally again.

Protx, the UK's largest independent payments service, handles secure credit and debit card payments for more than 10,000 retailers.

One small family lingerie firm which trades online told the BBC that the problems led to the loss of around 50 orders, worth an average of £50 each.

Protx apologised "wholeheartedly" for the problem.