Retailers' leaders are to develop a model for determining increases to the national minimum wage.

The British Retail Consortium will lobby politicians to adopt the concept, which aims to remove uncertainty surrounding the annual rise.

"We are working on a formula that will make a predictable link between the minimum wage and earnings, rather than the increase being a figure that the Low Pay Commission plucks out of the air," said a BRC insider.

Retailers had welcomed the latest increase - about 3% from October - but feared future rises might not be so moderate. The CBI has calculated that the minimum wage rose by 27% between 2002 and 2006 - faster than the average wage growth of 18%.

The March announcement of the rise also causes a headache, said the BRC, and gives little time before the next

financial year to plan ahead.