It looks like a Datura or Brugmansia. Both are closely related, are called Angels Trumpets and look very similar. As the flowers of Brugmansia normally hang down then I would say it's a Datura.

Thank you Myron I checked Datura in my book and it says it has spiny fruit, this doesn't it just has the delicate lantern shape with a berry inside.

Yes, you're quite correct. Angel's Trumpets have large spiny fruits that look like conkers in their shells and I missed this in your photo. Try Googling "Blaue Lampionblume".

Will do thank you again Myron :o)

That is Shoo Fly plant, Nicandra physalodes. It is an annual and it seems to self seed all over the place even where it has never been seen before.

Thank you Owdboggy I agree! I have looked on line and 3 names have come up but all seem to be for this plant!
the other common name linked to the one you mention is Apple of Peru.
The others are: Quicula Lobata Physalis lobata purple flower ground cherry - both came up when I googled Blaue Lampionblume as Myron suggested! Thanks to both of you for your answers - happy gardening!

Yes. I know it only a shoo fly and it pops up every couple of years or so in my garden.

This is the problem with common names Neellan, people call plants by different names and it gets confusing. I believe that Blaue Lampionblume is the German name for them. And yes, it is also known as Apple of Peru shoo-fly plant and there are probably many other common names for this species. The Botanical name for these species of plants as Owdboggy said is Nicandra physalodes. If you use that name then it's definitive.

By the way, it's called shoo-fly because It's a natural insect repellent. And it gets the name Apple of Peru from the area that it comes from and the little apple like fruit that it bears. Beware though, it is a member of the nightshade family so all parts of the plant are poisonous.

Thank you Pennyfarthing it is a pretty plant to have such an unpleasnt name as shoo fly!!

Thank you Myron for all that extra information that is great, it is nice to know I can now tell my neighbour - he grows it every year as an annual from seed.