Lottowyn, I would say not only workers of northern origin, but anyone who is not going to inherit a £800k 3-bed semi, would be interested in moving north.
The isolation works two ways:
The northerner can't afford a family home in the south-east. This was just about possible 30 years ago, I recall.
Anyone looking to move out of the SE can afford it, but they are put off by the job insecurity that comes with any change of employer nowadays, and the lack of alternative employment in the regions. Then there's the lack of liquidity in the property market, a potential trap.
All of which is detrimental to the UK economy. In the past, big corporations like BSC and ICI offered the chance of internal career moves around the country, to the benefit of all parties, and with less risk incurred by employer and employee. This has largely disappeared.