Hello - I have a Ford Fiesta Diesel. It won`t start in cold weather, but in `normal` conditions, it starts first time. Is it the battery?

Dont know much about diesel engines but if i had this prob wit my petrol id try:
-changing all HT leads
-make sure you've got a decent battery
-try taking off distributor cap and drying it out
-spray everything like HT leads wit WD40 to dry out