A tube coupling system (1) for a pressurised fluid system comprising a coupling body (3) for receiving a tube (5) of a pressurized fluid system, a leakage seal (7) for preventing fluid supplied from the pressurized fluid system via the tube to enter the coupling body (3), a gripping member (9) for gripping the outer surface of the tube (5) received in the coupling body (3), and an environment seal (11) for preventing intrusion from outside of the coupling body (3), characterized in that said environment seal (11) is at least partially displaceable and arranged to be pressed at least partially off a sealing seat when there is internal fluid pressure in the coupling body (3) resulting in a fluid stream out of the coupling body (3) and said fluid stream to the outside of the coupling body (3) indicates a leakage from the pressurized fluid system.