A method of using a downhole tool assembly in removing a casing from a well on a single trip, comprising the steps of: a) providing a downhole tool assembly on a work string, the downhole tool assembly comprising: a downhole pull tool, the downhole pull tool having an anchor mechanism and at least one piston member moveable between an extended position and a retracted position, the at least one piston member is coupled to the work string; a spear tool; a motor unit; and a cutting device wherein the motor unit is configured to rotate the cutting device; b) lowering the downhole tool assembly into the well through a first casing string wherein the casing to be removed is a second casing string located through the first casing string in the well and the spear tool, downhole pull tool and motor unit are located above the cutting device with the downhole pull tool located above the spear tool; c) actuating the downhole pull tool to grip the first casing string; d) actuating the motor unit to rotate the cutting device to cut the second casing string; e) latching the spear tool to the second casing string to grip the second casing string with the spear tool; and f) actuating the downhole pull tool to pull the work string to dislodge the cut second casing section, the downhole pull tool pulling the work string and cut second casing section upward in the well; characterised in that: step (d) comprises actuating the cutting device by pumping a fluid into a through bore of the work string to deploy at least one knife in the cutting device; and the downhole pull tool grips the first casing string while the motor unit rotates the cutting device to cut the second casing string. a) providing a downhole tool assembly on a work string, the downhole tool assembly comprising: a downhole pull tool, the downhole pull tool having an anchor mechanism and at least one piston member moveable between an extended position and a retracted position, the at least one piston member is coupled to the work string; a spear tool; a motor unit; and a cutting device wherein the motor unit is configured to rotate the cutting device; a downhole pull tool, the downhole pull tool having an anchor mechanism and at least one piston member moveable between an extended position and a retracted position, the at least one piston member is coupled to the work string; a spear tool; a motor unit; and a cutting device wherein the motor unit is configured to rotate the cutting device; b) lowering the downhole tool assembly into the well through a first casing string wherein the casing to be removed is a second casing string located through the first casing string in the well and the spear tool, downhole pull tool and motor unit are located above the cutting device with the downhole pull tool located above the spear tool; c) actuating the downhole pull tool to grip the first casing string; d) actuating the motor unit to rotate the cutting device to cut the second casing string; e) latching the spear tool to the second casing string to grip the second casing string with the spear tool; and f) actuating the downhole pull tool to pull the work string to dislodge the cut second casing section, the downhole pull tool pulling the work string and cut second casing section upward in the well; characterised in that: step (d) comprises actuating the cutting device by pumping a fluid into a through bore of the work string to deploy at least one knife in the cutting device; and the downhole pull tool grips the first casing string while the motor unit rotates the cutting device to cut the second casing string. step (d) comprises actuating the cutting device by pumping a fluid into a through bore of the work string to deploy at least one knife in the cutting device; and the downhole pull tool grips the first casing string while the motor unit rotates the cutting device to cut the second casing string.