I've just done this curry and I can say it was by far the nicest curry I've done.
Here's what I've done slightly differently:
For the tomato I blended a tin (240g) of plum tomatoes with a tsp of tandoori massala. Instead of BE spice mix, I used c2g mix powder (without bassar) and instead of 2 tsp of chili, I used 1 tsp of kashmiri chili powder and a pinch hot chili powder. A bit more than a tbsp of coconut. Instead of sugar, I used demerara and a tiny bit of lemon extra at the end. Half-way thru the cooking add half-onion cooked into the mix.
It was fantastic, though my mouth is still burning :-)
Thanks for the recipe.