A safety scalpel comprising: a handle having a front end and a rear end with a blade secured at the front end, the handle comprising: first securing formations including a forward end stop, a rearward end stop, and a guide channel provided between the forward end stop and the rearward end stop, first and second notch formations (66, 68), a forward cooperating notch, and a rearward cooperating notch; and a protective guard having a leading end and a trailing end, the protective guard comprising: second securing formations including a tooth configured to slidably move within the guide channel and to engage with the first and second notches, and a manually releasable locking catch, wherein the guard is slidably secured over the handle in a mounting zone defined between the forward end stop and the rearward end stop of the handle, the guard being manually operable between an extended position in which the first notch formation is engaged with the tooth and in which the guard projects forward of the front end to surround the blade, and a retracted position in which the second notch formation is engaged with the tooth and in which the guard is retracted from the front end to expose the blade for use, wherein the rearward cooperating notch is configured to engage the manually releasable locking catch and to releasably lock the guard in the retracted position, wherein the guard and handle are configured to permit securing of the guard to the handle such that, during assembly, the leading end of the guard is introduced over the rear end of the handle followed by forward movement of the guard so that the tooth of the guard is brought into cooperation with the forward end stop, the rearward end stop and the guide channel of the handle to hold the guard captive in the mounting zone when the scalpel is not positioned in an extended terminal locked position, the first and second securing formations being configured to permit entry of the guard into the mounting zone, wherein the extended terminal locked position of the handle is defined by the first securing formations on the handle and the second securing formations on the guard, wherein, in the extended terminal locked position, the guard is located forwards of the extended position and it is substantially impossible to unlock the guard from the extended terminal locked position, and wherein the guard is further configured to be releasably locked in the extended position via operation of the manually releasable locking catch and the forward cooperating notch. a handle having a front end and a rear end with a blade secured at the front end, the handle comprising: first securing formations including a forward end stop, a rearward end stop, and a guide channel provided between the forward end stop and the rearward end stop, first and second notch formations (66, 68), a forward cooperating notch, and a rearward cooperating notch; and first securing formations including a forward end stop, a rearward end stop, and a guide channel provided between the forward end stop and the rearward end stop, first and second notch formations (66, 68), a forward cooperating notch, and a rearward cooperating notch; and a protective guard having a leading end and a trailing end, the protective guard comprising: second securing formations including a tooth configured to slidably move within the guide channel and to engage with the first and second notches, and a manually releasable locking catch, second securing formations including a tooth configured to slidably move within the guide channel and to engage with the first and second notches, and a manually releasable locking catch, wherein the guard is slidably secured over the handle in a mounting zone defined between the forward end stop and the rearward end stop of the handle, the guard being manually operable between an extended position in which the first notch formation is engaged with the tooth and in which the guard projects forward of the front end to surround the blade, and a retracted position in which the second notch formation is engaged with the tooth and in which the guard is retracted from the front end to expose the blade for use, wherein the rearward cooperating notch is configured to engage the manually releasable locking catch and to releasably lock the guard in the retracted position, wherein the guard and handle are configured to permit securing of the guard to the handle such that, during assembly, the leading end of the guard is introduced over the rear end of the handle followed by forward movement of the guard so that the tooth of the guard is brought into cooperation with the forward end stop, the rearward end stop and the guide channel of the handle to hold the guard captive in the mounting zone when the scalpel is not positioned in an extended terminal locked position, the first and second securing formations being configured to permit entry of the guard into the mounting zone, wherein the extended terminal locked position of the handle is defined by the first securing formations on the handle and the second securing formations on the guard, wherein, in the extended terminal locked position, the guard is located forwards of the extended position and it is substantially impossible to unlock the guard from the extended terminal locked position, and wherein the guard is further configured to be releasably locked in the extended position via operation of the manually releasable locking catch and the forward cooperating notch.