I agree with Infragreen, looks like some type of slime mould. It could be Enteridium lycoperdon, this is what the 'Encyclopedia of Fungi of Britain & Europe' has to say:
" Comparatively large, cushion-like, whitish bodies with a somewhat rubbery feel, breaking down to reveal reddish-brown spore mass; on dead wood generally , though often still standing"
Here's a pic I found on the web:
Described as "soft to the touch as if filled with fluid"