Dying Laurel Hedge - HELP!

Hi,

A beautiful laurel hedge that borders my house is sadly dying. As someone with little gardening knowledge, I was hoping someone may be able to help. 

For some reason the reason, the leaves are going black and dying. It seems to be spreading and when I have trimmed back dying branches, I have noticed that the central stems are black and powdery.

Could this be a fungus or bacteria?

Any ideas on what to do would be really appreciated.

Thanks


Av