A downhole apparatus for location on a tubular, an assembly, and a method of use are described. The apparatus comprises a body with a throughbore configured to receive a tubular, and at least one swellable member that comprises a material selected to expand upon exposure to at least one predetermined fluid. The swellable member is arranged to provide a seal between the body and a tubular on which it is located during use, for example in a micro-annulus between the body and the tubular. Advantageously, the apparatus may be configured such that the body is moveable on the tubular before expansion, which may permit the apparatus to be slipped or slid onto the tubular into its desired location. The apparatus may be configured to rotate or slide on the tubular.