Please can someone identify this plant.

Looks like the petals curve backwards slightly, in which case it could be H. kouytchense

Hypericum "Rose of Sharon"

Google it and see if googled pictures matches with yours

I've just noticed the reddish streaks on the buds - I think the one I've mentioned has more red buds, though they open and look like these flowers.
Just had a trawl through various pics - some show the variety I mention with red buds, others the buds are yellow and I can't tell if they have these stripes on them.

Thanks Aimankay but I've already googled and have just got rather confused so I've turned to GoY's experts!
Hi Bamboo.....mmm not sure about kouytchense. Just looked it up and it seems to be more of a larger shrub than mine and is described as 'arching' whereas this has upright stems with clusters of flowers on the ends. It's not at all woody and the flowers are small, only about 1" across.

Ah, not described as arching in my book - its those streaks on the buds, should be definitive, but there are so many varieties of hypericum out there - doesn't seem to be a Hypericum Society or Association like there is for Hebe and Fuchsia or anything either, been looking. Fractal might know...
Just to add to the confusion, there is something called Spotted Hypericum, or Hypericum punctata, which can have spots or streaks on the buds, so whatever this is, its bred off that I'd think. Be interesting to see what berries it forms and whether its deciduous, semi evergreen or evergreen.

What about Hypericum Calcynum ?

Thanks Marie but it's definitely not Calycinum, I've had that in a previous garden.
Many thanks Bamboo, you have been busy and it seems identification isn't going to be easy. I think we're agreed it's Hypericum at least so maybe I'll just have to settle for that!

Those leaves look quite thick in texture compared to most hypericums - are they, Lily?

I see what you mean Bamboo but no they're not at all thick, just average thickness. Now that it's come into flower a bit more it's actually quite disappointing. When the first flowers opened I thought it would be more striking than it is. I'll post another photo tomorrow with it next to something common for size comparison.