Paul Krugman: Agglomerating A Revolution:
Nicks, Crafts and Wolf... argue that the cutting edge of Britain’s Industrial Revolution, the cotton textile industry, benefited hugely from agglomeration.... Crafts and Wolf suggest, in effect, that at least some of England’s comparative advantage in cloth came from external economies, not underlying national characteristics.... It’s interesting to at least contemplate the possibility that but for the accidents of history, cotton cloth might have been made by the banks of the Tagus rather than in the region of the Mersey.
Only if you give Portugal (i) Britain's super-cheap coal, and (ii) have it gain Britain's early-nineteenth century seaborne empire and thus have Britain's real wage levels--only then is even the agglomerated early-nineteenth technology profitable when deployed, and only if you deploy early-nineteenth century technology can you develop mid-nineteenth century technology.
And the problem was that it didn't have the coal, and the fact that it had to defend its border (not terribly successfully) against Spain meant that it couldn't focus on gaining and keeping the empire.
Truth to tell, as Bob Allen points out, only Britain, the Ruhr, and Silesia had the geography to give them cheap-enough coal; and only Britain (and, I suppose, Ireland) had both the ports and the islandishness to allow them to focus on dominating the world of the commercial revolution.
And if we had somehow had an 1805 in which the Portuguese navy won the Battle of Trafalgar while the coals were still in Newcastle, what would the world of today look like?