A London authority said on Wednesday it had imposed “temporary measures” around a new mural by British street artist Banksy after it was defaced within days of appearing. Islington Council, in north London, said it had erected fencing and camera surveillance and ordered visits by community officers to manage on-lookers to help protect the artwork. The stencilled mural of a person having spray painted tree foliage onto a white wall behind a leafless tree, appeared on a street near Finsbury Park this week. The enigmatic artist appeared to confirm his role in the creation, posting before and afte…