steveinsussex as this is a weather forum ..most will stick to the met office definition which is as follows :
"at the Met Office, we use a meteorological definition of the seasons. By the meteorological calendar, the first day of winter is always 1 December; ending on 28 (or 29 during a Leap Year) February.
Meteorological seasons consist of splitting the seasons into four periods made up of three months each. These seasons are split to coincide with our Gregorian calendar, making it easier for meteorological observing and forecasting to compare seasonal and monthly statistics.
The seasons are defined as spring (March, April, May), summer (June, July, August), autumn (September, October, November) and winter (December, January, February)."