It is bright and pretty Art, so don’t worry what it is, just enjoy the lovely colour it brings to your garden>:-)
Look at Hypericum Patulum, rare dwarf hypericum. Can’t do links on phone 
Aka St.John’s Wort.
TessA, l have got one of those in my garden, (see pic) but that has larger flowers than the mystery plant has and the leaves are different.
Twink, l am no quitter! I never give up!
By hook or by crook, l will find out! 
TessA, Thank You. 
l have grown the ones l call Hidcote from cuttings and their leaves are dark green. The flowers seem to be the same but differ in size.
I did look up the rare dwarf one you suggested bur again, it seems to have the dark green leaves.
Here is a pic of the leaves…
Paint them dark green!
It could be an Audrey 2!
By coincidence my son, who has moved house recently, sent me this photo of a shrub flowering in his garden and wondered if I knew what it was. I have no idea but is the flower anything like your flower, Art?
Mags, That is the same as the ones that are already growing in my garden. I have two, that l grew from cuttings.
I only know it as a Hidcote.
You mean like this, Gorgeous looker?
Whilst we are at it.
Does anyone know what these are. I went to a funeral and we were all given a packet of seeds to grow in memory of the deceased lady.
I planted them and they look like cabbage or sprouting plants to me!
That’s interesting Art, I googled for more information …
Could mystery plant have grown from a seed or similar from the Hidcote?
Mags, l have now decided, my mystery plant might be a Potentilla?
I remembered, l had also grown two of those from cuttings but they hadn’t done so well, as they were also planted in an area where there were trees.
I have just looked at one of them now. It’s a poor thing with lots of dead branches, so l am going to move it.
The leaves on it are the same as the mystery plant but much tinier.
The blue bits are slug pellets. 
You don’t say!
That looks more like it Art, a pretty plant too. 
Now the flower has come out Artangel I am having doubts. It could be a hypericum, the flower is very much like it. I thought I was sure, but …
Have to keep on searching a bit longer.
No idea what the other plant is - but it looks a bit like some sort of leafy vegetable.
Aerolor, It’s a mystery!
I have loved this thread. It has been like a mystery ‘who dunnitt’ or waiting to find out the sex of a new born baby!
Mags, I think it probably is. They are pretty plants and the bees etc like them!
Look like very young kohlrabi to me