I am done with interview&Medicals since April 2010. Why it is taking time to receive a request to send my passports for the visa

I need to know why it is taking too much time to get any feedback from the Canadaian Embassy in London about the status of my application for immigration for Canada while I am done with the medical exams? So far no answers about when I should send my passports to get the visas for landing? Please, advise me for the same.