Please can someone identify my rapidly growing plant? I bought it at the Horticultural Society stall on Open Gardens day as an unnamed small plant in a pot. Since then it has threatened to take over! I think it might be a squash or pumpkin or something from that family.
Fiona
PARWICH.ORG 
The leaves are not deeply cut but more rounded, and the developing fruits are quite round, both of which rule out the marrow, courgette and spaghetti squash end of the squash range. The leaves are more like pumpkins, but there are a fair number of other winter squashes that would also fit, see
What’s Cooking America
http://whatscookingamerica.net/squash.htm
About.com Local Foods
http://localfoods.about.com/od/wintersquashpumpkin/ss/Types-Of-Winter-Squash.htm
YouTube
I suspect that, unless the person who donated the plant to the stall sees this post, you may have to wait until the fruit is a bit bigger to make a successful identification. At least it won’t keep growing beyond the first frosts, and hopefully you will get some meals out of it. Unlike courgettes, you wait till the winter squash has a hard skin, and you just eat the flesh. If they ripen well, the winter squashes keep longer than the summer squashes, such as courgettes, into November and maybe beyond.
It could alternatively be an ornamental gourd, then you can dry and paint the fruit for use as Christmas decorations. However your photos don’t fit with either of the two groups of ornamental squashes considered on eHow (see http://www.ehow.com/how_7639243_identify-ornamental-squash.html). The flowers are yellow, but the stems look smooth, not hairy.
Thank you for all that information Peter. I look forward to seeing how the fruits turn out. I was hoping the triffid breeder might read the post and respond but as you say I shall just have to wait and see!