Jacko,
I had a job recently with a national housing developer, they had left the roof off of one block of housing too long, the result was mould growth on all the timbers in the roof space, not a pleasant odour by any stretch of the imagination. However I treated with a mould-killing chemical available from any builders’ merchants and then sealed the timbers with varnish. They paid me, so it must have worked!! You know how these developers love to find any excuse not to settle their accounts!!! Hope this helps pal.