Firms are paying their subcontractors an average of three weeks late, compared with two weeks late a year ago, according to research from credit rating agency Experian.

As well as settling bills after the agreed date, the research found that companies are extending subcontractors' payment terms from 30 days to 60 or 90, writes Building magazine.

'The problem for small suppliers is made worse because they are often under pressure to settle their own bills quickly,' said Tony Pullen, managing director of Experian's business information division.

This is bad news for those who have campaigned to improve payment practices in construction. Building spoke to Suzannah Nichol, chief executive of the National Specialist Contractors' Council, who said: 'It's incredibly frustrating. How do they think those down the supply chain can manage an extra 21 days, particularly in these times of the credit crunch? It just proves what we have been saying for some time. It is unacceptable.'