Hi all sorry if this has been covered a hundred times, my internet connection here is work is temperemental at best and is failing fast so must move quickly.
Over the past 3 days my engine has cut out 4 times, all in 5th gear at reasonably low RPM (first time was at 80MPH

), and very suddenly - without warning at all really.
I am now very worried as 3 of the occasions it has cut out have been on the very busy, fast and twisty Cardiff Bay link-road and losing power, steering going heavy and brakes becoming less powerful are bad combo.
When it cuts, the engine is just below the middle of the gauge (which seems normal for mine), the revs drop to zero instantly while the speedo ticks down slowly. The alternator and oil pressure lights come on immediately (ignition still in the second position), and it takes a good 15 minutes before I can restart it. Before this, the engine will turn and turn but not fire. Last night it fired back up within 5 mins but died again instantly.
I thought it could be dodgy fuel from Tesco as I had the first problem just after adding a tenner of 95 RON, but having burnt that off and getting some optimax last night (just in case) it died again this morning so its not bad fuel.
When its restarted it runs absolutely perfectly, still getting the good MPG, still pulls strongly - all seems absolutely normal.
Would this indicate ignition or are there other things I should look for? Will be getting it on the tech2 over the weekend hopefully.... very worried indeed as its plain dangerous

Anyone else had a similar thing? Any suggestions please?
Thanks for reading
Worried Alex