industry - PhD student, issued contract at year 3 which will sign over intellectual property. Is it legal?

I'm EPSRC (Engineering and Physical Science Research Council, the biggest UK funding source in the sciences and engineering) funded. Several months into my PhD an industrial sponsor came along. In exchange for additional funds they wanted me and the other PhD students in our group to spend some time during the PhD at their sites and work on industrial problems. This is known as a CASE award. I'm not sure what the university signed, but I have not signed anything. It was a verbal agreement with my supervisor.

I'm now in my 3rd year and writing up. The industrial sponsor has decided to renew their agreement with the university and just issued me with a contract (it states the university and industrial sponsor have agreed upon additional clauses as of early 2015). The clauses/contract that I've been asked to sign states that I will give the industrial sponsor all my intellectual property (to which I currently own) generated over the course of the last 3 years. It also states that the industrial sponsors will review all publications and stop me publishing anything they think will give them a competitive edge (Note I'm not and have never used any of their data, resources or industrial knowledge/work/ideas etc. this is my own work) - I'm just about to publish the remainder of my PhD and then submit my thesis in the coming months. I was in good position to finish early and focus fully on moving to the industrial site for the remainder of my PhD and work on the projects the industrial sponsors wanted me to look at. Clearly for any projects done while there, the IP would belong to the industrial sponsors - however they want everything, including the stuff I did before they even got involved!

Additionally signing the contract means that they can make my thesis closed - i.e. future employers are not allowed to see it. This could damage my future prospects as I was also looking at work outside of academia and they will no doubt want to know what I've been up to. This was never part of any agreement and I would have never taken on a PhD with these terms. Academia is all about the publishing and the free flow of ideas - this all makes me a very cheap slave!

Legally, where do I stand? I understand that as an employee issued with new contract I would have to either sign or walk away, unless it goes against the heart of the contract. But I'm a student and I'm in the last few months of my PhD, if I walk I get no qualification.

I've been told that they can't make me sign it - but won't go into detail as to whether it will affect my PhD or not? Again I'm EPSRC funded the industrial sponsors have paid me extra around 10% of the EPSRC stipend in exchange for me spending several unpaid months at their site working on projects of their choice. I've been told by my supervisor that it's in my best interest to stop resisting and ultimately sign the contract. Can they do this three years in? Has anyone been through anything like this? Anyone have any advice?