I'm having the same problem. At first I thought it was just cos I used BP Ultimate (I pulled into a service station, BP, first day I got the car in the middle of nowhere with an empty tank and I opened the fuel door and it said "Optimax Only" in big letters....)
It's been happening less (I think) since I put Optimax in but it happened again yesterday, mostly sitting at lights, and once when I braked hard to give way just before a right turn and it stalled.
I have an atmo BOV, is this causing it somehow?
The only answer I've found to avoiding it at lights (most common time to stall) is leave a good 6 feet to the car in front, if I feel it start to stall take foot off brake and roll a couple feet forward, brings the revs up and stops it stalling. Also using handbrake at lights keeps the revs higher.
Was gonna bring it up when I get the car checked over by mechanic in a couple weeks.