  Exploiting the residual gauge freedom in the formulation of constrained KP
hierarchy a number of new integrable systems are derived including hierarchies
of Kundu-Eckhaus equation and higher order nonlinear extensions of
Yajima-Oikawa and Melnikov hierarchy. In the multicomponent case such gauge
freedom generates novel multicomponent as well as vector generalisations of the
above systems, while the constrained modified KP hierarchy is found to yield
another set of equations like derivative NLS, Gerdjikov-Ivanov equation and
chen-Lee-Liu equation depending on the gauge choice.
