visa problems WHM

Hi. I am currently living/working in the UK on a WHM visa which expires in Jan 2009 (although I am only permitted to work until Jan 2008)
My grandad was born in the UK, I understand I can get an ancestry visa because of this, I have all proper documents to prove this.
I have looked on the website for Ottawa but cannot seem to find any info on if they can void one visa and let me apply for another one? can anyone help me out?
is it possible to apply for an ancestry visa after you have already applied and been accept for a WHM?

You need to have the original birth certificate of your grand dad showing that he was born in the UK and the connection between you and him. You can apply for ancestry visa after getting the WHM but from your home country.