Hi huggybear,
That sounds like a bit more than a couple of shovels for gardening. Are these tools you use for your business, or are you just really very expensively handy around the house.
If the latter, then just specify them on your household insurance, making sure that the cover extends far enough.
If however they are for business (also in the workshop is for business then this brings the building insurance into question too) then you would need a policy that covers business equipment.
I won't profess to have a detailed working knowledge of who covers what, but I do remember Zurich were always pretty flexible with covering stuff outside of the "always occupied 2 up 2 down", so they could be a good starting point.
mr tom