Blackthorn - one of the first to blossom

Blackthorn is a native tree and very common for hedging, particularly for traditional hedgerows.  It flowers much earlier than hawthorn and most of the other blossom producers.  It also flowers before it produces its leaves so you get this mass of dirty-white flowers at the roadside which seem really unexpected when all the other trees are still just winter bare. It produces dark blue berries in later summer that are the sloes that make sloe gin famous.

For bees, (if it warm enough for them to venture out ) blackthorn is a great source of both pollen and nectar; where this is planted as a main element of hedges it can be available in considerable quantities but each small tree will be covered in flowers so even a single a single one in a garden will be great source.