@JillThePlantKiller It depends on what part of the UK you live in, your local microclimate and the weather that year. I gauge spring by my own random method, not by what it says on the calendar.
Early spring - winter flowering jasmine, snowdrops, catkins,
Mid spring - primroses, blackthorn, daffodils, camellia, cherry blossom
Late spring - tulips, cowslips, apple blossom, bluebells, honeysuckle
Early summer - roses and a whole heap of other stuff
But they all gradually merge from one to another so there is no definitive date I don't think. The only actual date I use is that you need to have pruned your roses by Valentine's Day.
The seasons in the UK are changing anyway - my rosemary comes into flower six weeks earlier than it used to. 40 years ago it was around new year, and it now starts flowering in mid November and goes all the way through to March. It gets some flowers in mid summer but its main flowering period is winter. Good for bees who have woken up too early.
Hawthorn is also called May blossom as it is supposed to flower in May. Round here all the hedges have been in flower for several weeks already.
Gardeners can't really follow dates as such, you have to rely on instinct.