More often, the question is, "What is keeping it from flowering?" The flower buds form soon after bloom, in early to mid summer, so any pruning after that may keep it from blooming the next spring. For the same reason, a roaring cold storm off the ocean could do the same thing, if you consistently have tip burn by spring. Do you know which species of Philadelphus it is? Also, which part of the UK are you in? The north coasts of Britain could easily be marginally too cold for the evergreen kinds of Philadelphus.

Are you sure its a Philadelphus - I ask because these shrubs are not evergreen in the UK, they lose their leaves in winter, so if yours doesn't, maybe its not Philadelphus.

Sorry, Bamboo, my memory was playing tricks on me! I remembered evergreen Philadelphus from visits to coastal northern California, but on investigation, evergreen species are few and far between, and probably hard to find in the UK!

Impossible, though possibly in a heated greenhouse somewhere

P. mexicana might work somewhere in coastal southern England or Ireland, but probably iffy there, too.

Alan it would be good if you could add a photo to your question so that we can confirm what your shrub is.

Just had another idea.If you Google Evergreen shrubs for seaside gardens you'll find some suggestions that you can compare with your shrub to try to identify it.
If its grown quite tall and has silvery leaves it might be Eleagnus ebbingii. That does have very tiny white flowers, very easily missed but highly scented