Theoretical calculations were used to evaluate the response of a tridimensional (spatial) external electric field on the binding energy $\left(E_b\right)$, polarisability $\left(\alpha \right)$ of a hydrogenic donor impurity and diamagnetic susceptibility versus the dot width $\left(L_d\right)$ and the tridimensional electric field intensity $F$, and the impurity location $\left(x_0\right)$ in a $GaAs/G{a}_{1-x}A{l}_{x}As$ double symmetrical quantum dot. The numerical computations were accomplished by utilising the effective mass approximation and the variation method. Our calculations showed that the polarisability diminishes as the applied tridimensional electric field F rises, especially when the dot width is large. Nevertheless, this polarisability is independent of the tridimensional field strength F when the confinement is strong. It has been observed that the degeneracy of the binding energy is broken under the effect of a tridimensional field F. Furthermore, in the absence of a tridimensional field, the diamagnetic susceptibility ${\chi }_{dia}$ is symmetric in relation to the centre of the barrier material, having two peaks. However, this symmetry is broken when a spatial electric field is applied.