Can you please post a picture? I don't understand how it can have buds & foliage yet not flower. It does take its sweet time. Mine also has buds that are ever so slowly advancing. Just keep it well watered & don't do anything rash. It will eventually flower.

I don't know where you are in the UK, and you haven't said if its Hydrangea macrophylla or not, but assuming its that particular variety, your plant is in the ground, and you're anywhere south of Watford, the likelihood is the lack of rain has caused this. Now that it has rained, and specially if you supplement with water, you may find the buds open up, so long as they haven't given up and dried out. Flowering shrubs will sacrifice their flowers when they're under stress in order to survive, and drought is a stressor.

As the name implies 'Hydrangea - water vessel,' This is one plant that must never lack water.