Its central England temperature (CET) record has been, on average, 29 days longer than the reference climatology period 1961-90, according to figures it released on World Meteorological Day (23 March).
The Met Office records the length of the growing season as part of a set of UK climate statistics based on temperature. The CET record is the longest continuous temperature record in the world, with monthly temperatures dating back to 1659 and a daily series back to 1772.
Dr Mark McCarthy, manager of the Met Office's National Climate Information Centre, said: "Between 1861 and 1890 the average growing season was 244 days and measuring the same period a century later the average growing season had extended by just over a week. For the most recent 10 years between 2006 and 2015 the average growing season has been 29 days longer at 280 days when compared with the period between 1961 and 1990."
The figures also reveal that six of the 10 longest growing seasons in the CET record sequence have occurred during the past 30 years, with 2014 having the longest of all at 336 days.
The CET series also shows that the number of days of air frost has been declining over recent decades, with the 1961-90 average exceeded only in seven years since. Met Office weather station data shows that the average number of annual days of air frost across the UK during the period 2006-15 fell by a sixth compared with the period 1961-90.