Redundancy query - Suitable alternative V leaving

Hi I hope someone can advise me. My department were I work has gone through a re-structure and I decided to take voluntary redundancy. Date to leave is early November. A job within the same company came up so I applied and they have given it to me and my VR has been withdrawn.

Yesterday got a phone call from a company I applied for a job at weeks ago and had given up on asking me for an interview. The date for this is 3 days before my notice period for my current job comes up.

My question is, if I was to be offered this post at the new company can I turn around to my current employer and tell them I have changed my mind about the new position within the company and please can I re-instate my VR or is it too late now I have accepted this suitable alternative?

Thanks