If it sold or was marketed by an agent in the last couple of years, bother Rightmove and Zoopla should have these details (assuming the agent put it on there, and the seller hasn't requested them to be removed. Land Registry will tell you only if it has been sold since 1995.
Zoopla
Go to the "house prices" section and either type in the road name (at which point the first part of postcode should come up), or type in the postcode.
Go down to the house number, and click on it. Below the section that says estimated sales value, there will be a second section called "sales price history" and a third section called "history on Zoopla". If sold price paid will be in section 2, and marketing price together with pictures and floor plan should be in section 3.
Rightmove
You need to go to the browser site (not the app), and go to the section for "sold house price data". Again put in either address or postcode, then navigate down to the house number. If it's been sold since 1995, you'll see the price paid, and the marketing material linked. If not, it won't be there.
Land Registry
You can go to their sold price data section, and type in the postcode or Road name to find out how much a sale in the past 15 years was for. However you won't get any data on price if it didn't sell, so only use this method if you know if definitely did sell.