I assume you mean the flowers aren't opening properly before they die off. Where are the dahlias, in pots or in the ground? And if you live in the south, have you been keeping them well watered? Or do you live somewhere its been wet windy and cold? (So much easier if you post the area or county you live in under your profile rather than just the country).

I have the same problem...some are opening, others are in full bud and then dying off. We had a spell of very dry, hot weather, followed by high winds and some heavy rain. I suspect I may have over-watered though! Is that feasible, Bamboo?

I live in North Licnonshire and they are the ground. Thanks

You can't overwater, Izzy, as long as there's good drainage in a pot, without a tray at the bottom, or if they're in the ground, unless you're growing them in a bog!
Dahlia flowers do this in 3 circumstances - when its pretty wet and windy, when its very hot and very dry, or, sometimes, infestation in the flowers, usually earwigs, sometimes other insects. This assumes the leaves are perfectly healthy, with no brown marks or disease signs.

Just looked again today...very healthy leaves..in proliferation...but buds are now brown! This summer is freakish...I have primulas flowering today as well!

My primulas are flowering too, but that's not unusual at this time of year, believe it or not!