Detailed experimental studies of ion heat transport have been carried out in JET to explore the Te/Ti dependence of ion heat transport in ITER relevant range of parameters (Te/Ti 1) using low rotation plasmas with dominant ion cyclotron resonance heating (ICRH) to avoid the coupling of the effects of Te/Ti and rotation which affected previous experiments. This experimental set up has led to an accurate determination of the ion temperature gradient (ITG) threshold at varying Te/Ti, offering unique opportunities for validation of the well-established theory of ITG driven modes. A rather mild decrease of threshold with increasing Te/Ti in the interval of ITER interest was found. The new experimental result has found good agreement with theoretical predictions based on quasilinear fluid and linear gyro-kinetic models.