What is ‘prompt’ when it comes to payment?

Is there an identifiable trend in terms of those most responsible for late payment? At one time it was local councils that were so noted but in many parts of the country that seems to have improved. Is it now the case that the bigger the brand the slower you can expect to get your money or are Unilever’s and Sainsbury’s payment terms of 90 and 75 days respectively, as highlighted in the FPB story, just par for the course?