Finally got round to making it:
I didn't want to risk wasting a full mash, so I used 3kg John Bull light malt extract, 30g goldings, 30g fuggles & Safale. Plus two tea-spoons of crushed dried chilli peppers.
It has quite a kick to it, but not much flavour. No taste of malt and hops. My wife drank 1/4 pint before she could taste the chilli and described it as "not unpleasant". It reminds me of ginger beer. The hot after taste lasts quite a while. I've tried it now: I'll not be making any more!
If you're thinking of trying it, I'd suggest only one tsp of chilli.
Chilli beer