did you try jumping the battery?
Likely the battery. The starter motor uses many hundreds of amps to crank. Much more than all the other electrical systems on the car put together.
When a battery is close to death, the 1st symptom will be that the cold cranking amps ability of the battery in cold weather will substantially drop. Could have become bad in May and lasted all through to this cold snap.
I'm sorry but many hundreds of amps to crank is nonsense. Most average cars wont even reach 100A when cranking.
All fixed, I Charged the battery then it started fine, I have now replaced the battery which has cost another £100 added to all the money i have spend on this stupid car, Now i need to get an Anti-pollution error fixed that only allow's 2900rpm's before i can sell it, I had this problem before with it and spent around £800 on getting a new high pressure pump fitted (peugeot wanted around £1500) and the message came back again about 6 months ago and won't go.
DO NOT BUY A PEUGEOT 307!!!
Thanks for all the reply's though guys you definetly helped me fix the problem.
A piece of test equipment measured my 1598cc motor consuming about 270A before Christmas, and this was cranking slowly on a battery which needed charging.