I planted a philadelphus about 3 tears ago, this year it had black fly which I killed with a spray- then a couple of branches fell off, and now although it has made new growth still hasn't produced i single bloom. I am very dissapointed as this has to be one of my favourite shrubs- shall I dig it up and compost it.

Give it one more year Elaine.  Sounds like it had a traumatic time this year.  The important thing is if you have to prune it, then make sure you do it at the right time of the year.... as soon as it has finished flowering or as soon as it should have flowered.  June/July time.  Never prune in the spring otherwise you might take away any shoots that it planned to produce flowers on. 

Thank you Pamela, is it to late to prune now?

It is really too late because there is no growing season left for it to make new growth for next years flowers.  Because it's an early flowerer (May/June) it doesn't have time to make much growth in the spring before it is expected to flower... it is really just producing leaves in the spring.  Hopefully you will get flowers on the growth it has made this summer.  Even with the awful summer we have had it will have made some new growth.