What's wrong with my beef?

[ninnypoo]

I put a brisket joint in the slow cooker at 1pm today using this recipe: allrecipes.co.uk/recipe/17545/riko-s-juicy-slow-cooked-roast-brisket.aspx

Helpful DP turned the slow cooker up to high at 5.45pm. It's now really tough and nowhere near falling apart! Any ideas how to salvage?

It needs longer to cook, turn back to low and leave for another 3 hours. Not much good for tonight's dinner thou.
You could try adding some wine vinegar so the acid helps break down the meat too