In this paper the digital and analogue performance of double-gate tunnelling FET, DGTFET, is reported, when a pocket of different dielectric is inserted near the source, drain or both. The variation of these pocket lengths and their relative shift to the edge of source or drain region affects device performance. The investigated performance parameters include the ON/OFF ratio, the maximum cut-off frequency, fT, the subthreshold swing, SS, and the ambipolar current, Iambi. With the aid of TCAD simulator, the effect of pocket parameter variation is studied. Our study shows that when the main gate dielectric is hafnium dioxide, the source pocket is favored to be of low dielectric constant and high width. However, for the drain case, it is better to have shorter pockets with a low dielectric constant. The investigation shown here proves that pocketing the DGTFET can enhance its whole performance in terms of investigated parameters.