K11 Starting Problem

Hello All!
We have a 1997 K11 Micra which has been an amazingly reliable car having done only 62k miles from new. Normally, it starts first time...every time. However, this week during the cold snap, it refused to start.
The engine would crank over absolutely no problem & sound like the odd cylinder was trying to fire every so often...but it would NOT run.
I checked No.1 spark plug & found a healthy spark there. All the plugs seem ok....although they were very wet with fuel. I also got the ECCS system into its diagnostic mode...which just reported code '55' (All circuits ok?)
I did finally manage to get it started by cleaning & pre heating all the plugs....but it was VERY reluctant to run.
After 15min of running...it now seems ok again.
Very perplexed as to why it wouldn't start as the car is normally SO reliable & predictable.
Any ideas guys?