It looks like a courget or marrow flower.

Hi Bulbaholic, Funny you should say that as my Father in law said it looked like a cucumber. I had a whole tray of these that I grew in my tiny greenhouse. I only grew them from the dead heads of flowers from my garden , but I def didn't have these last year so it's a mystery where they've come from????

Did a squirrel sneak in and hide some seeds it got from somewhere else? Maybe a neighbour had a neglected marrow or squash plant with an overlooked fruit that the squirrel raided? It's definitely marrow family - could also be courgette or squash.

Well whether it be marrow, courgette or cucumber you should get some nice fruits off it.

Hi Grannyb, I have just been in the garden & all the flowers have closed up ....is that what usually happens?

Hi Beattie, We don't have any sqiurrels around here that I know of. It's all a bit of a mystery to me !! My garden will look strange if they are marrows etc. as they are all planted amongst my flowers! I best inform my sister too as she had quite a few too.
Thank you all for your replies once again.
It's nice to know if there is something I need to know I can ask on here :)

I had a whole lot of melon plants and tomato plants that came up in the flower beds where I'd spread home made compost one year. The compost contained kitchen waste, including melon "innards" and gone-off tomatoes and it obviously didn't get hot and kill the seeds.

I have two composters, and when I can't get any more in the second bin, I empty the one that was filled first. Anything that isn't composted quite enough just gets popped back in & I start filling again. This means that I spread home made compost at all sorts of times of year. The unexpected melons & tomatoes came up at the end of summer and were killed by frost.

Jay, It's either courgettes or another case of 'Invasion of the body-snatchers', keep the doors and windows locked!

They could be marrows, jay, as the flowers look too big for cucumbers. You'll just have to wait and see! I don't suppose the flowers will mind sharing the ground with these monsters, and anyway, the bees from the flowers will help to pollinate the Marrows/courgettes. I had a load of small grape vines growing after I'd used some garden compost, so obviously my compost bins don't get hot enough, either! Who cares? The plants seem to do well growing in the compost, and that's the important thing.
Anyway, good luck with them, whatever they are. You can make a very tasty meal from marrow stuffed with meat and veg, so keep them growing! Annie (Cumbria)

Thank you all for your replies. I'll wait to see what happens & whether I get anything other than the flowers.......watch this space!!!!