Could be a physalis, they have purple lantern 'fruits'. Although don't eat them until you can get a definite confirmation!

We got asked this same question earlier today - and one of our members identified the plant as Nicandra physalodes.

Haha, Beattie - I got there first this time! (sorry, Sylvia, I couldn't resist that!)

Thank you Spritzhenry I know many plants but have never come across this one before and I am still curious to know how it enede up on my allotment!
I have looked it up in my books and it is a member of solanacae group. It says that it is the 'apple of Peru ' There is no photo in my book. How did you know what it was?

Darn, I was cooking! Another one to you Spritz. :-)
We're getting asked about this plant all the time at the moment. It must have rained Nicandra seeds one meteorite spattered night, like in "The Day of the Triffids". Perhaps that's what inspired John Wyndham.

Sylvia, I only knew because Beattie identified the plant in an earlier question! Glad we were able to help, though. :-))

I reckon the seed is not destroyed by the composting process and is arriving in people's gardens in compost, rather like Oxalis cornuta does.

At least it's an annual so more easily controlled.

It does produce a huge number of seeds though.

Could chop it down before it sets seed.

So i assume that that is different from the Physalis. Although there were similar things on a friends allotment that had the Chinese lantern styley about them... but they were the edible type.

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I thought Physalis lanterns are orange?

Very different to Physalis and poisonous.