Possible means testing of IB

I'm sorry if this has cropped up elsewhere but if a decision is made to means test IB (and presumably carry over to ESA C) will it have to go through Parliament and due process or can it just 'happen'? It will mean that people who have worked and paid NI won't be entitled to benefits until their savings have gone and presumably the law regarding occupational pensions that began before 2001 will also change and be classed as income so some people will never qualify for any sickness benefits. I think they will go ahead with this but how quickly can it be enforced?