A downhole tool and a running tool are described, each being retrievably settable within a suitably sized cased well bore without the need for any interaction between the downhole tool or the running tool and any restrictions or recesses in the well bore to land, anchor or retrieve either tool. The downhole tool has a mandrel, an anchoring means mounted on the mandrel and controllably reconfigurable from a retracted configuration to permit movement of the downhole tool through the well bore to a radially expanded configuration for releasably engaging the cased well bore. The downhole tool anchoring means is reconfigured using a ratchet that resists movement of the tool anchoring means from the expanded configuration back to the retracted configuration until a release mechanism is released to allow retraction of the downhole tool anchoring means and retrieval of the downhole tool from the well bore.