Clay soil advice

Hi all
due to a bit of inexperience and over enthusiasm I have managed to bring  about 2-3 inches of clay and clay interchange layer to the surface whilst digging the over the new allotment .The soil is made up of good top soil to about a spades depth but is 1/2 a spade in places. The area affected is aprox 10ft by 20ft.  Any advice will most grateful .

Add as much compost or rotted manure as you can - and rake the worst lumps  (the ones that wont break down when bashed) to one side.
It'll be a bit rough this year - probably best to plant things in it rather than trying to sow seeds but will improve each year.

I wonder how long it takes to break up the clay with organic matter - our site has been allotments since between the wars and the soil is still solid with big lumps of bright orange stuff. Dread to think what it was like for those first plotholders 

Depends on how much organic matter you apply each year. I think people under-estimate just how much volume of soil there is in a full size plot and thus how much organic matter/sharp sand/whatever is needed to make a significant difference.

See other thread posts on here re- clay soils, but yours sounds just like when I dug over what was a previous field area to make my raised beds. I had just about the same amount of topsoil as you and brought some sub-soil (alluvial silt) to the top when digging. Get some gypsum and also some grit/sharp sand then double-dig your beds. Fork over the bottom of your trenches and addthese with any compost or organic material, plus mix these  in all layers as you refill. The grit gives instant results, not sure how long gypsum takes to work but should do it this season. Organic matter will take a bit longer.

Thanks All for the wonderful advice
I will add muck and sand as I will keep this patch fairly fallow this year as the front half of the plot is a lot better
I should I plant a green manure once I have worked the sand and muck in?

I was also told today that the previous tenant only worked the front half of plot so that explains why the shed was halfway down the plot and not at the back as required by council.

Monty Don on GW last week suggested mushroom compost is particularly good as organic matter to add to clay soil.  The lime particles in it help improve the clay structure (flocculation, if my memory from several years ago is correct).

It is indeed called flocculation.

I've got something similar on mine - but things do grow very happily in it!

I've got 3 daleks of manure rotting away, and will be working green manure this year plus any well-rotted manure I can get my paws on. Plus free topsoil from someone near me who is digging out their lawn.

The beds I double-dug and added manure to last year are so much lighter than the new ones I am diggng at the minute. And they have loads of worms and very few/no weeds 'cos I was meticulous about getting all the blasted roots out when I dug. *smugface*

I had very clayey soil. I've been working some of it for five years, the rest of it for six. I've just done a quick calculation and reckon I've added nigh on a tonne of muck a year (rabbit and sheep). I have around 250 square metres under cultivation. More muck would have been better in the early years, but it's not easy working it in, especially when you're expending a lot of effort digging.

My patch is getting towards a decent standard, though I still get a rock hard crust if I don't keep on top of the hoeing (which I never do...).

Keep adding as much organic matter as you can manage. If you get gypsum, make sure it's suitable for agricultural purposes.