Sycamorework

Looks like an old Shaggy Bracket fruiting body to me. Shaggy Bracket causes white rot, so a good crown reduction may save the tree snapping where the brackets has grown.

Where are you thinking of going to work? And what quals do you have?

Is this the first year it’s happened?

Have you added anything new near the tree?
Could there be anything kept on the concrete area collecting water and distributing it to the tree, a grit bin for example?

If there’s no immediate danger, I’d say leave the tree alone. It certainly looks like it’s ready to fall though and if work is necessary, maybe consider a monolith? Leaving some habitat behind.

I don't pretend to know a lot about this subject but could it be a cultivar , like a fern leaved beech , is there a graft line ?

Cristata was the closet guess I had whilst looking through books. If you google it, however, it shows very little.

It looks like a Robinia pseudoacacia, false acacia, covered in ivy.

I have seen the exact same thing today whilst out and about.

Looks like a Grey willow.

How big is the turfed area? And how much did you pay per Sq.m for it?