Control valve assembly and fuel injector incorporating a control valve assembly

A control valve assembly (36) for controlling fuel pressure in a control chamber (34) of a fuel injector (30). The control valve assembly (36) comprising a valve member (46) arranged in a bore (42) provided in a valve housing (44), at least one of the valve member and the valve housing (44) being moveable with respect to the other, wherein the valve member comprises a fuel-receiving cavity (78) arranged to receive fuel that distorts at least a portion of the valve member so as to increase an external dimension thereof.