In effect it would be like any devaluation, were it to stay the same for a long time, which I don't believe.
However it would mean that whatever we sell abroad is cheaper from the point of view of the buyer.
This should make it easier to sell more.
As you rightly said there is some offset by the costs of raw materials, however The UK manufacturing industries tend to specialise more in the sectors where high value is added so that basic raw material costs are not as important to the end price as they once were.
Take it all as a package, put on your optimistic specs, and think that it's not all bad.