If its Lavender stoechas, or one of its cultivars (French lavender) then it'll be the lack of good weather this year.

My Lavender (English and French) are just coming into flower. I would say in my garden that the 'English' varieties are doing much better than the French varieties this year. Munstead, an English variety, is looking great at the moment.

Thank you all for your comments. Think I will invest in an English variety then I can monitor both varieties.

Even my English lavenders are very late flowering this year - they only came into flower 2 weeks ago, when normally, I'd expect flowers in late May which I'd have clipped off and they'd be on their second flowering now. A bad year for 'mediterranean' style flowering shrubs.