While previously mills have offered to hold stock at wharf locations for an unlimited period, it is understood that paper will now be invoiced on the 60th day.

One industry insider said the change for stocking paper was mainly in the cut-size paper sector, and had been going on for a while now due to challenges with cashflow.

Malcolm Sinclair, marketing director at independent Scottish paper manufacturer Tullis Russell, said: "It is clear that all along the value chain, given the current tough economic times, people are realising that while we are all keen to win new business as well as retain existing customers, any additional services including stockholding need to be paid for somehow."

Justin Hobson, marketing director, Fenner Paper, said: "Mills offering to hold stock at wharf locations for an unlimited period defies good business practice. How can you sit on stock for an unlimited period? It's ridiculous. Storage is not a free commodity."

He added that mill stocks, wharf stock and payment terms were all part of purchasing negotiations.

"Some customers may take a cash discount if the mill offers it, some mills will invoice from date of delivery and others from the end of the month in which the delivery was made.

"These are all factors (as much as the price) that are discussed or negotiated before an order or contract is put in place – it's basic buying and selling."

Paper manufacturer Stora Enso couldn't comment at this time, while UPM and Sappi were unavailable for comment.