what does a statutory tree mean ? we have one on the pavement outside and council says it is a statutory tree ?

I've never heard of a "statutory tree", but there are trees with Tree Preservation Orders, which cannot be removed or even pruned without the permission of the council.

It means it is a protected tree that basically has rights to be there...If it fell down, died or got damaged, the council would have another tree planted in it's place.

This usually means there are rules to do with Tree Preservation Orders and/or Trees in Conservation Areas placed on said tree, if you do any unauthorised work on these trees the council can fine you allot of money so its always best to seek advice.

As stated before, statutory trees are installed by the relevant district council in compliance with organisations like wildlife trust, woodland trust etc. What I mean by this is many diverse species of tree are installed in urban areas, providing habitat for a myriad of insects, birds and other relative wildlife. For this reason trees normally envoke a mandatory TPO or legislation preventing unauthorised tampering or alteration.

You cant do any works to that tree without council permission