What's the starting symptoms, needing a number of cranks before turning over, starts first crank but rough running , white smoke on start up ?
I find my td5 lately takes a little longer to start in cold weather but it always starts on first turn of the key ( i do have a original battery and pushing 15 years and powering a electric winch and 400w of roof lights think it's due a new one when it starts showing its age)
Without seeing it I would check the battery is in good condition ( as well as clean and regrease Earth points and battery terminals) as low temperatures will really test the batteries ability to start a cold diesel.
If in doubt try halfords or local garage to carry out a battery test .
Greg