[double-happiness]

OK thanks all, that's reassuring.

I am liking the idea of removing turves and stacking them to rot down... I was thinking more of digging the grass out by the roots with a fork but it might actually be easier to use a spade to dig squares of turf out.

Just leaving the paths as grass and mowing them could be a good move too.

Scaffolding plank edges sounds neat but it might not actually be necessary, I will see how things go.

Mind you if the weather keeps up like this I have a feeling I am going to spending more time on here than on the allotment 

[Trikidiki]

You could stack the turves to make the walls of a temporary compost bin, somewhere to put all the really rough weeds you'll be taking out. Then you can cover the whole thing tightly with black polythene and leave it for a couple of years as suggested above. Perhaps even put down some weed membrane before you start so no roots can grow down below the heap.