Where are your boundaries? The airport now says Teesside but would it be inside or outside the new PRTeesside? You could be in trouble at the very start calling it Teesside.
Even if you're going by the tighter definition of Teesside, limiting it to Middlesbrough, Stockton-on-Tees + Redcar and Cleveland, it would still be larger in size than 15 or so sovereign nations and larger in population than nearly 30 sovereign nations.
As poor as our area is in relation to a lot of the country, I expect our economy would still be signficantly larger than some of the poorer island nations too.