Is my tree done?

I've got a lavender tree (I think anyway, in summer it's got the most beautiful purple colours, better and deeper than all the others in the area) and I've been struggling for a few years now with suspected dead limbs, ivy trying to choke it from the neighbours garden at the rear (who are literally smackheads, won't do a thing unfortunately) however last night parts of it lit up when I had the flood lights on and I'm pretty sure it's fungus growing on it. I've gone out this morning and got these close-ish ups. The tree does have buds ready for spring but is this fungus and needs the limbs chopping back to the trunk to save it? UK based if that helps.