The nominal operation of the LHC foresees injection of beams capable of damaging Transfer Line (TL) and LHC equipment if uncontrolled losses occur. The SPS-to-LHC TLs are thus equipped with a passive protection system: a set of collimators (TCDIs) aimed at intercepting particles with large amplitude and/or mis-steered beams. An overview of the present system is given, with particular emphasis on operational aspects and experience: accurate procedures for beam based alignment of collimators and setup validation, dedicated system of interlocks for jaw positioning and overall collimator functionality, issues encountered during operation and improvements. In view of the improved beam brightness foreseen by the LHC Injectors Upgrade (LIU) and High Luminosity LHC (HL-LHC) projects, the upgrade of the system is presently under study. Main design challenges, simulation tools and results are summarised: system layout and phase coverage including geometrical uncertainties, choice of suitable materials able to stand the head load and provide sufficient attenuation, protection of downstream devices.