May be mice
As for the trapping i'll do the right thing and get advice off the allotment committee of what to do if it is rats.
Hope this eases everyones minds.
Edds second picture is mice poo, baza described rats poo. best not to use an humane trap, there is only one way to dispose and its not nice.
It can be hard to distinguish mammal poops.
There are a couple of ways you could find out though without trapping. One is to set-up trail camera and see if you can photograph the culprit. (worth it if you have other uses for a trail camera, not really worth the expense if it is a one-off unless you can borrow one).
The other is to use a sand bed. If you can put out a shallow tray with some sand in right where you saw the poop, you might get some footprints (a tray full of wet clay soil works just as well). It is easier to tell the difference between a hedgehog and a rat by the footprints.
Hedgehogs tend to poop when they're feeding and as they wander aroud so you usually only find one dropping at a time.
Rats' droppings tend to be in accumulations.
When I had rats their droppings were oval, smooth and quite shiny, like dark grains of wheat in size. mouse droppings are similar but smaller. I am hoping I have a hedgehog around as I occasionally find some droppings which do not look similar. Much darker, rougher in texture, slightly larger in size. Someone suggested it might be from a weasel or stoat.
Here is a couple of photos of the droppings . What does everyone think
They are just over an inch long