Background to the invention The use of piezo-ceramic actuators in the engagement of rotating parts has been previously disclosed. Whilst such devices offer effective locking, their dimensions are not suited to applications where access is limited, or where a traditional mechanical key barrel is employed. It would be advantageous to have a clutch mechanism whose outer dimensions are sufficiently compact to permit use within a standard mechanical lock cylinder profile, such as the widely used Europrofile. Further it is especially preferable if the mechanism fits within the lock barrel space, which is typically around 12.5mm diameter and 30mm length. For such a solution to be effective it is essential that the actuator itself does not form part of the locking structure. According to the invention there is provided a piezo ceramic bender whose motion is used to interfere with the path of a sprung detent, where the detent has insufficient force to connect the rotation of a first input part to a second driving part. The interference produced by the actuator increases the detent force such that the behaviour of the system is changed. In order that the present invention be more readily understood, an embodiment thereof will now be described by way of example with reference to the accompanying drawings, in which:- Figures 1 and -2 show perspective views of a basic form of cylinder lock useful in explaining operations of the present invention; Figure 3 shows a perspective view of part of a cylinder lock according to the present invention; Figure 4 shows a perspective view of another part of a cylinder lock according to the present invention; Figure 5 shows an end view of the parts shown in figures 3 and 4 assembled and in a first condition; Figure 6 shows an end view of the parts shown in figure 5 in a second condition; Figure 7 shows a perspective view of an actuator for use with the assembly shown in figures 5 and 6; and Figure 8 shows an exploded perspective view of the actuator shown in figure 7 and a barrel of a cylinder lock. An embodiment of the invention is now described with the aid of the accompanying figures, using the Eurocylinder as a model, but the principles apply to any substantially narrow cylinder configuration. The form of the Eurocylinder profile (10) is defined by international standards, but there is freedom within these dimensions for any feature deemed appropriate. A typical barrel diameter of 12.5mm is used within the main chamber (11) diameter of 17mm. In normal locking systems, such as are shown in figures 1 and 2, the cylinder barrel (12) is coupled to the actuating tongue (30) by an axial clutch, such that whichever end of a pair of barrels is permitted to rotate by the insertion of the key connects to the actuating tongue and permits operation. If this feature were not provided it would be necessary to operate both barrels to free the actuating tongue. This is standard design and is mentioned purely as background, without detailed illustration thereof. In the traditional situation the locking action is therefore provided by any number of pins placed in shear between the barrel (12) and the profile (10), running in bores (13). According to the present invention and referring to Figures 3 and 4, the actuating tongue (30) is not rigidly connected to the modified barrel (20), rather it is substantially free to rotate upon a suitably dimensioned bearing surface (22). A mechanical coupling between the barrel (20) and the actuating tongue (30) is provided by means of a sprung rotary pawl (40). Depending upon the design choices there may be any number of such pawls as space will permit, but a particularly convenient number is 2, disposed on the same pitch circle and interfacing diametrically with detent features (34) on the internal hole (36) of the actuating tongue (30). The detent features (34) provide an engagement for the pawl (40) but also provide an angled face (35) such that rotation of the barrel relative to the tongue generates a vector that tends to force the pawl (40) out of the detent features (34). The pawl (40) is pushed into the detent features (34) by a biasing spring (50) which also serves to link the two parts together. The actuating tongue (30) has a minimum operating torque that is provided by a spring detent or friction washer assembly of any suitable design. The minimum operating torque of the actuating tongue (30) is substantially greater than the torque required to force the pawl (40) out of the detent features (34), so under normal circumstances the user cannot operate the actuating tongue by rotating the barrel. It will be appreciated that in the configuration where there is a single rotary pawl (40), only one corresponding detent feature (34) would be provided on the actuating tongue (30) for engagement by the pawl (40). Furthermore, one end of the biasing spring (50) would be connected to a fixed point, for example a fixed pawl, but would achieve the same effect of pushing the pawl (40) into the detent features. The pawl (40) is shaped to provide a projection (41) which is received in the detent feature (34), an engagement feature (45) and a curved, free pivot feature (43) which is arranged to engage with the internal bore (36) of the tongue (30). Approximately at the centre of the barrel and with its main planes axial to the barrel is mounted a piezo ceramic bender (60). The bender may be of any suitable design, but, as shown in Figure 7, is preferably based upon two plates of bulk ceramic (61) mounted to a thermally matched substrate (62), formed into a hairpin configuration, with a conductive tape overlay (63) to maintain function in the event of fracture, and where the whole assembly is protected from the environment by an appropriate coating. The mounting of the bender (60) to the barrel (20) is preferably resilient and permits some rotary freedom of the device. The fixed end (66) of the bender (60) is mounted to the barrel (20) and the free end (64) projects past the mounting point and enters the space occupied by the actuating tongue (30). The free end is provided with a bar element (64) capable of withstanding compressive forces and acting under the control of the bender (60). Based upon the scale of the system as defined by the Eurocylinder profile, the engagement of the pawl (40) will be about 0.75-lmm on each side. Control features (43) are provided on the pawl (40) that reduce the gap between the two diametrically positioned pawls to the engagement plus a simple clearance of about 0.5mm. The bar (64) is formed such that when the actuator is not operated by the application of an electrical charge it does not enter the locus of motion of the pawl control features (43), so that the pawl engagement features (45) can be pushed out of the detent features (34). Accordingly, in this configuration, when the actuator is not operated, the actuating tongue (30) is capable of rotating upon the bearing surface (22) of the barrel (20). When the bender is charged the bar (64) moves into the locus of motion as indicated by the arrow in Figure 6 and thus prevents the engagement features (43) exiting the detent features (34). Accordingly, this prevents the rotation of the actuating tongue (30) upon the bearing surface of the barrel (20). The plane of movement of the bar (64) is in the same plane as the plane of the motion of engagement features (43). In this manner, the bar (64) is movable between a first and second position. In the first position, the free end is positioned between the diametrically opposite pawls so as to form a mechanical linkage in order to positively inhibit radially inward movement of the pawls. In the second position, the bar is removed from the position between the pawls along the same plane of motion as that of the engagement features thereby enabling inward radial movement of the pawls. As is apparent from Figure 5, each pawl engagement feature (45) is formed of an abutment surface (45a, 45b) such that in the first position (as shown in Figure 6) each edge (64a, 64b) of the bar (64) abuts the corresponding abutment surface (45a, 45b) of the pawl engagement feature (45). The mechanical linkage formed inhibits any inward radial movement of the pawl (40). The abutment surface (45a, 45b) is shaped so as to exert a compressive force on the edges (64a, 64b) of the bar (64) when an inward radial force is applied in the first position. The force exerted on the bar (64) does not push out the bar from the first position. Accordingly, the bar (64) remains in a stable condition in the first position and is only moved to the second position when the electrical charge is removed from the bender (60), and the actuator is not operated. It will be appreciated that in the configuration where there is a single movable rotary pawl (40), the same effect will be achieved when bar (64) is in the first position. That is, the bar (64) will abut the corresponding abutment surface (45a, 45b) of the pawl engagement feature (45) and therefore inhibit the radial movement of the single pawl (40). It will be • apparent that although there is only one radially movable pawl in the single pawl configuration, the other pawl will be fixed but is provided with similar pawl control features (43) as the movable pawl. However, the projection (41) is not provided but the control features are designed such as to enable the pivoting of the fixed pawl within the pivot feature (43). The bar (64) is reinforced to have a strong section (65), capable of withstanding the compressive force of an applied torque. The maximum specified operating torque under most standards for a lock in an installation is 3Nm. Assuming a friction compensated interaction angle of 45° and a pitch circle for the detent interface of 11 mm, a torque of 3Nm translates to a radial force on the detent of 272-300N. If the contact area of the Given the high electrical charge on the piezo actuator, it is preferable for the strong section (65) to be an insulator. A suitable material for the strong section is an engineering polymer, such as glass filled ABS, or an engineering ceramic, such as alumina. In circumstances where it is preferred to power the system to lock, the position of the actuator can be altered such that the strong section (65) interferes with the pawl motion locus in the unenergised condition and is moved away when powered. In a further embodiment it is possible to take the normally locked condition as described above and create the detent features (34) on the profile barrel (10) such that the barrel is immobilised when the actuator is unpowered. In this arrangement the actuator cam can then be connected to the barrel in the normal manner.