A tourniquet includes a strap formed of a flexible material and shaped as a long, thin and generally flat body having a first surface and an opposed second surface, and an array of ridges extending transversely, substantially along most of the first surface. The tourniquet head includes an insertion mouth and within the mouth a flexible support and a plurality of teeth formed on the flexible support. The flexible support and the plurality of teeth providing an insertion channel in the tourniquet head for tightly receiving a free insertion end of the strap in a manner that enables the strap to be threaded through the insertion mouth with the plurality of teeth in the head being lockable on the ridges on the strap in a manner that enables a leading end of said strap to be ratcheted through the mouth in a locking direction only. A release lever enables the flexible support in the mouth to be pulled away from the ridges on the strap to allow for temporary disengaging of the teeth in the head from the ridges on the strap, to enable gradual and controlled releasing of tourniquet tension being applied on a body part to which the tourniquet has been mounted.