03 Micra K12 - Cranking but wont start when engine is cold

My K12 Micra has developed a Cold Start Problem that has me stumped !! Over Xmas, I noticed it was struggling to start first thing in the morning ... but would start eventually and run fine. But about a week ago, it just refused to start. Thinking it was probably the Engine Temp Sensor, I replaced that - but it has made no difference. Still no start when cold.

I've gotten around this a couple of times by removing the Spark Plugs, heating them with a blow torch and quickly putting everything together again. It then Starts no problem & runs great. No problem with starting or running when the engine is warm ...

Also, there are No DTC's coming up on code reader ...

Can anyone point me in the right direction ??

Thanks in advance.