Method of connecting a fitting to a tube element, comprising the steps of - inserting a tube element into a fitting, the fitting comprising - a fitting body, at least one bushing member comprising a bushing member body (52; 252), the at least one bushing member body being mounted on the fitting body, and the bushing member body having a tube fixing portion (56; 256) with a longitudinal insertion end for a tube element, and a mounting portion (53; 253) at longitudinal distance from the insertion end, the mounting portion (53; 253) having a longitudinal end inner face (54; 254), wherein the tube fixing portion (56; 256) comprises at least one tube hooking member (60; 260), the tube hooking member (60; 260) projecting from the tube fixing portion (56; 256) with a free edge (61; 260) facing the longitudinal end inner face (54; 254), and wherein the at least one tube hooking member is a flexible tab, with an inner hooking surface having a profile capable of irreversibly penetrating into a tube outer layer, - a locking member positioned on the at least one bushing member, wherein the locking member is adapted to move from a rest position, in which the locking member is positioned on the at least one bushing member without significant deformation of the at least one tube hooking member, to a locking position, in which the locking member presses radially against the at least one tube hooking member, so that the at least one tube hooking member is deformed towards the center of the fitting, to move into a hooking position, the locking member being in the rest position, - moving the locking member into the locking position, so that the at least one tube hooking member comes into the hooking position in which the tube hooking member is engaged in the tube element by radial compression of the locking member on the at least one tube hooking member, the inner surface profile of the at least one hooking member penetrating into a tube outer layer. - inserting a tube element into a fitting, the fitting comprising - a fitting body, at least one bushing member comprising a bushing member body (52; 252), the at least one bushing member body being mounted on the fitting body, and the bushing member body having a tube fixing portion (56; 256) with a longitudinal insertion end for a tube element, and a mounting portion (53; 253) at longitudinal distance from the insertion end, the mounting portion (53; 253) having a longitudinal end inner face (54; 254), wherein the tube fixing portion (56; 256) comprises at least one tube hooking member (60; 260), the tube hooking member (60; 260) projecting from the tube fixing portion (56; 256) with a free edge (61; 260) facing the longitudinal end inner face (54; 254), and wherein the at least one tube hooking member is a flexible tab, with an inner hooking surface having a profile capable of irreversibly penetrating into a tube outer layer, - a locking member positioned on the at least one bushing member, wherein the locking member is adapted to move from a rest position, in which the locking member is positioned on the at least one bushing member without significant deformation of the at least one tube hooking member, to a locking position, in which the locking member presses radially against the at least one tube hooking member, so that the at least one tube hooking member is deformed towards the center of the fitting, to move into a hooking position, the locking member being in the rest position, - a fitting body, at least one bushing member comprising a bushing member body (52; 252), the at least one bushing member body being mounted on the fitting body, and the bushing member body having a tube fixing portion (56; 256) with a longitudinal insertion end for a tube element, and a mounting portion (53; 253) at longitudinal distance from the insertion end, the mounting portion (53; 253) having a longitudinal end inner face (54; 254), wherein the tube fixing portion (56; 256) comprises at least one tube hooking member (60; 260), the tube hooking member (60; 260) projecting from the tube fixing portion (56; 256) with a free edge (61; 260) facing the longitudinal end inner face (54; 254), and wherein the at least one tube hooking member is a flexible tab, with an inner hooking surface having a profile capable of irreversibly penetrating into a tube outer layer, - a locking member positioned on the at least one bushing member, wherein the locking member is adapted to move from a rest position, in which the locking member is positioned on the at least one bushing member without significant deformation of the at least one tube hooking member, to a locking position, in which the locking member presses radially against the at least one tube hooking member, so that the at least one tube hooking member is deformed towards the center of the fitting, to move into a hooking position, the locking member being in the rest position, - moving the locking member into the locking position, so that the at least one tube hooking member comes into the hooking position in which the tube hooking member is engaged in the tube element by radial compression of the locking member on the at least one tube hooking member, the inner surface profile of the at least one hooking member penetrating into a tube outer layer.