Any suggestions how to remove this once the camshaft pulley has broken up?

Trying to remove the remains of the camshaft pulley so I can replace it, but can't move the bolt and got no way to hold the pulley (cos it's not there anymore!)

 

You will need to remove the rocker cover to gain access to the camshaft itself. on the camshaft there is 2 flats, a spanner does'nt fit it all that well to be honest (its not as flat as it could be). But you will get some grips or similar on enough to hold it while you crack the block.