It's Thai Dragon sweet chilli sauce (or similar), mixed with a little Maggi tamarind sauce and a dash of lemon juice Dave. This is the basis for typical BIR chilli dips hereabouts. May have read it on here somewhere. I add a bit of regular red chilli powder to give it a kick. Kashmiri chilli powder for colour (or Preema red). Other variations include mint sauce or ajwain. I got the Thai sauce from Farmfoods. 700 ml for £1.79, I think.
Rob