Zoopla allows a limited access to its API providing the latest property prices and area indices. I created a package in R that allows querying this database. See the GitHub documentation or zooplaR’s page for the latest info.
You can easily get prices in the last couple of months or years for a particular postcode, outcode or area:
View the code on Gist.
Given, the limit number of queries, it might be worth double-checking the results with the property widget offered by Zoopla (redirects to zoopla.co.uk).
It doesn’t have as many options as the API and obviously is not automatic but it’s worth using for a sanity check.