After purchasing a record image within the 1921 Census of England and Wales, you will land on what would have been the back of the household schedule, the primary part of the record that was filled in by those within the household. To see any of the other images including Address information, click on Extra (Address)
Extra (Address) is located within the filmstrip. You will then see an option to view the Front of the household schedule which includes the address information which you can access at no additional fee:
If you have closed the filmstrip this can be reopened using the "Open filmstrip" button at the bottom of your screen, or for smaller screens at the top next to Options.
Remember, you can download each page with the download button in the Options menu.
If you need to view the original image again to find the Extra Materials you can view records you have already purchased in My Records. Alternatively, you can search again and there will be a tick next to the image entry you have paid for.