Frost-defying fungus

I found this growing  on the  oakwood box around a raised bed in my garden.  Not sure what species it is. I think I need to make  a spore print. 

Sunday 10th Jan I have now done a spore print which  revealed lilac coloured spores, suggestive of Pleurotus ostreatus,  the Oyster Mushroom, which is edible and  often cultivated. 
I don't think I fancy eating my specimens, however.....