Process for the production of butenes and butadienes from waste plastics feedstocks comprising the steps in this order of: (a) providing a hydrocarbon stream A obtained by treatment of a waste plastics feedstock; (b) providing a hydrocarbon stream B; (c) supplying a feed C comprising a fraction of the hydrocarbon stream A and a fraction of the hydrocarbon stream B to a thermal cracker furnace comprising cracking coil(s); (d) performing a thermal cracking operation in the presence of steam to obtain a cracked hydrocarbon stream D; (e) supplying the cracked hydrocarbon stream D to one or more separation units; and (f) performing a separation operation to obtain different streams comprising isobutene, 1-butene, 2-butene, 1,2-butediene and 1,3-butadiene; wherein in step (d): •the coil outlet temperature is ≥800 and ≤850° C.; and•the weight ratio of steam to feed C is >0.3 and