Need a bit more info - is it in a pot or the ground, and have you pruned it at all - if so, when?

Its in the ground - never been pruned as I understood that pruning stops them blooming

You're right about the pruning, doing that at the wrong time will mean no flowers the next year.

I'm assuming the plant is growing normally and healthily otherwise, and it has no evidence of other problems, so the next question is, how much sun does it get? They like at least 5 hours sun a day, and if they're in a low light or low uv situation, they will grow, but won't flower. The next possibility is to do with feeding - nitrogenous feeds will mean lots of leaves but no flowers, and I don't know if you've been feeding it at all or what with. Very wet soils may cause the same problem.

If, on the other hand, its slow growing and looking a little bit less than healthy, perhaps the ph isn't right - they prefer limey or chalky conditions.

Thank you so much - I will look into that - maybe not enough sun ! and look into the feeding also