SteVAT

Hi everybody. My business is VAT registered. I have a couple of receipts from high street stores, one for various kitchen items (cutlery, placemats, lamp, etc) & one for garden products (chippings & membrane). All goods are for use solely in the business. Both receipts show the retailers' VAT registration numbers & details of the items purchased, but no analysis of the VAT amount or rate charged. Can I reclaim the VAT on these receipts at an assumed rate of 20% on the net amount, or do I have to get an actual VAT receipt which is, as I have no doubt you're aware, not always easy. Thanks!