The House Prices Index isn’t just one index of UK house prices. There are numerous and it depends on who has an interest in making prices appear higher or lower, what the UK average house price is.
When the HPI features on the news it’s usually the Halifax version. However, far from being maintained by humans, most of the index is compiled from sold prices which are then adjusted for whatever current trend the Halifax thinks is happening.
Here’s a link to the last one (Nov 2013).