Allotments 4 All

The leaf is like a marrow or pumpkin, and the fruit is about the size of a small football, olive green (I think) in colour, spreading at a rate ok knots

Hi Tuffy and welcome to the forum!      I have separated and moved your post to where you may get more replies.
Was the plant self set?

pumpkin and squash spring up on my allotment. The seeds don't rot very well in the compost bins

Welcome to the site tuffy.  I agree with alkanet that your plant is probably a squash or pumpkin.  It could even be a round courgette.  You may have more of an idea when the fruit gets bigger. 

It could be a cross so may not resemble it's parents. 

search KABOCHA in google image,  and see if IT matches. your pumpkins.  ir is a green. pumpkin

As long as it's not Shark's Fin Squash.... 

The marrows and pumpkins cross very freely with each other and I've never found the offspring to be worthwhile.  If it's self-sown I wouldn't expect it to be very interesting.

Round courgettes are very rampant as are the dreaded Sharks Fin Squash (ask Pumpkinlover)

Quote from: shirlton on September 06, 2013, 06:36:23
Round courgettes are very rampant as are the dreaded Sharks Fin Squash (ask Pumpkinlover)

Unfortunately not everyone on this forum appreciates the wonderful Sharks fin melon. Many of last year's fruits still adorn the bedroom windows!

Anyway your fruit should be edible whatever whoever its parents are! 

What do you mean "the dreaded sharks fin squash".  It was the only one I managed to grow last year and I didn't even realise I had got anything more than leaves.  Managed to lug about 20 or so home after giving away the rest to fellow plotholders.  They keep well and no one wants to pinch them from your plot.

Quote from: lottie lou on September 06, 2013, 10:06:27
What do you mean "the dreaded sharks fin squash".  It was the only one I managed to grow last year and I didn't even realise I had got anything more than leaves.  Managed to lug about 20 or so home after giving away the rest to fellow plotholders.  They keep well and no one wants to pinch them from your plot.

It's a shame that some of our friends have such a blinkered view of this wonderful plant Lottielou, never mind we know!!
Having watched "Grow your own" it makes me appreciate this fantastic easy to grow and productive squash and how lucky we are in this country. Personally I feel a mission coming on as with just a bit of effort it makes a lovely and nutritious meal and if grown more widely a lot more people could eat healthily and cheaply!

(jumps off soap box!)