cutting out when reversing, plus 'white smoke'

sorry if this is in the wrong place

yesterday after driving around for some time, having done at least 50 miles, so engine nice and warm, i went to reverse out of a parking space to have it stall and die

took about half hour to restart, then only when key pushed right forward for longer than normal, started with cloud of 'white smoke' from exhaust then ran ok

this morning started first time, no smoke or halting, drove around parking and driving do shopping etc, first time i go to reverse, cuts out, keeps restarting but immediately cutting out and producing 'white smoke' from exhaust

Got rac out, who say theres plent of fuel getting to injectors and pump is working fine - explains 'white smoke' is unburnt fuel- start everytime using restart spray, but wont keep running

no warning lights, filled up with deisel yesterday, 29.85ltrs so not empty, only happened both times in reverse

car now towed to garage but any ideas what i can expect? I know no time is a good time for a breakdown but mil in hospital after heart attack so i need car on road asap

thanking you in advance