Oh, the "London Weighting" idea again. Not really a bad idea as the reality is that wages are so inflated in the South, especially in London, that the minimum wage their needs to be quite a bit higher than elsewhere. Otherwise we'll reach a point at which the economy of the North ends up suffering for the benefit of London (again...) or a situation in which the poor of London end up suffering in order to help the economy of the North.
I would be against any actual cuts in the minimum wage anywhere, but only out of principle.