Just moved to new house and have found this all over soil any idea what it is It's heavy and crumbly and loos like polystyrene but isn't

Could it be chalk?

is it damp ? id imagine its a fungi ? is there plants growing anywear near it ? is it a new build ? what does it smell like ?

Garden lime - for a veggie plot?

That looks like fairly fresh compost over the ground, so I'd go with fungus and it's helping to break down the woody bits in the compost. Break it up and fork it into the compost where it can do its job.

Left over cement from the Builders maybe? They can't always be bothered to remove it,so bury it instead..as we found out with ours.!

If it were fungus, it wouldn't feel heavy, and when you crumbled it, it would have a 'mushroomy' smell. More likely detritus left over from the builders which has been chucked on the soil. You can check if its chalk by trying to 'draw' with it on stone or paving. If you can mark out a hopscotch square with a lump, its chalk...