If you've got 80p in Gateshead, you've got the same spending power as someone in London who's got £1. Why, then, should we have a national minimum wage?
Brown's proposals to raise the NMW to £6 an hour across the country benefits those in Wales and the NE and NW, Labour's traditional strongholds, but does little to help businesses in those regions. If £6/hr were a fair rate in London, the government's own figures suggest that £4.80/hr is the right rate for the NW.
Indeed, the research was commissioned by Brown himself - when he argued that national pay grades in the NHS and public services were inappropriate, that a £40k salary goes a lot further in Gateshead than Guildford, and pledged to introduce regional differentials that recognised differences in the cost of living.
Except of course when Labour needs to buy votes.