Thanks for all the replies and the very helpful link.
I wasn't sure whether being dry rather than moist would have been an issue but if you can use it straight away, I'll just bag it up and put it to one side until the polytunnel is up and running.
No wood shavings or sawdust in there, just a bit of straw but mostly just pellets.
I had this down as a rainy day job but I need to crack on so although it's stayed dry despite forecast I've got about half of it in bags now, just stopped for a brew.
Thanks again all!