The present invention provides a process for the preparation of high molecular weight crystalline Polyethyleneterephthalate (PET) using up to 50% of Post consumer recycled PET flakes along with Pure Terephthalic Acid (PTA), Isophthalic Acid (IPA) and Mono Ethylene Glycol (MEG) as a virgin raw material, in the presence of a combination of catalysts and additives to obtain an intermediate prepolymer heel having a low degree of polymerization further subjecting to autoclaving to yield an amorphous melt and followed by solid state polymerization.