"Paying the congestion charge has always been a slow, irritating, process," said Angie Bray, Conservative congestion charge spokeswoman. "Ken Livingstone likes it that way because the hassle deters some people from travelling - and makes extra revenue from fines as people forget to pay. Yet we now find more than 40 per cent of payment outlets are not open at agreed times. By driving around trying to find a payment outlet that is open, users are actually increasing congestion."