Just to add to the confusiion:
I spoke with a guy today ( ebay trader) who I was going to buy a starter from.............
He asked if the starter was slower turning in colder temperature, which it is. Not a battery prob as thats new and has been checked anyway. He suggested wrong viscosity oil! Good thinking..... So bought some 5/40 oil today and a new filter. Will change tomorrow and see if it makes any difference....