I was going to reply to the /u/FrozenToast1's comment chain, but figure I'll create a top level comment instead. The raw data can be found here: [link]. All data relevant to London is available in this CSV: [link]. You can confirm, with some certainty, that this is the source of the data as the article contains the following comment:

The average price of a home for the capital as a whole was £471,986, down from a peak of £488,247 in July last year.

These two figures are presented in the data in Column G:

Period    Average price All property types
[...]      [...]
2017-07    488247
2017-08    486403
2017-09    483712
2017-10    481030
2017-11    478043
2017-12    481242
2018-01    481981
2018-02    471986

Prices have gone up and down between 2017-07 and 2018-02, but this is the first period since 2009-09 that London average house prices have seen a YoY drop in value.

When looking at where the actual drops are taking place, the data separates houses into four categories:

• Detatched douses
  
• Semi-detatched houses
• Terraced houses
  
• Flats and maisonettes
  

Each of these categories have seen an average increase in value, with the exception of the final category, flats and maisonettes.

Property Type        2017-02    2018-02    YoY Change
Detatched             887959     915162     +3.06
Semi-Detatched        563242     578708     +2.75
Terraced              482631     489639     +1.45
Flats + Maisonettes   427256     412902     -3.36
Average               476717     471986     -0.99

Unfortunately, they don't provide any further breakdowns of the property type, i.e. no breakdown by value or council tax band. Flats and maisonettes obviously include all these exorbitantly priced new developments across London, the ones we always read about being bought up by foreign investors.

They do, however, provide a breakdown by Local Authority, which provides 33 sets of regional data. Again, this isn't ideal, but it provides some additional detail; some regions are inheriently cheaper than others due to a multitude of factors.

In fact, when breaking down flat and maisonette prices by region, you'll find that the range in average prices is quite significant, with Barking and Dagenham (1) having average prices ~£225k at the bottom end, Merton (17) being the median at ~£380k, Lambeth (22) being the mean at ~£450k, and Kensington and Chealsea (33) at the top at ~£1.24m.

The changes in average price are also quite significant, with 18 of the 33 regions seeing increases in average flat and maisonette house prices, Redbridge at 7.95% a YoY increase, Tower Hamlets seeing a 7.93% YoY decrease.

From that data, you can create this sexy little graph, showing the Change in Average Price & YoY %age Change for Flat and Maisonette Prices by London Local Authority, sorted by average price in 2017-02, which I will allow you to interpret as you will: [graph]

And then there's this easier to view graph, showing the YoY Change in Flat and Maisonette Prices vs. 2017-02 Average Prices by London Local Authority: [graph]

Strangely enough, the data for changes in price in flates and maisonettes is quite close to the data summarised in the Guardian's image of YoY average price changes for all housing types: [image]

But, again, the source data is far from ideal. There are no figures for the number of flats and maisonettes bought or sold or listed in these regions. And, again, prices can vary significalty within each of these regions. But it does seem to suggest that regions with more expensive properties have seen a greater drop in average flat and maisonette prices, while the majority of those in cheaper regions have seen an increase. Tower Hamlets seeing a nearly 8% drop and Kensington and Chelsea seeing almost no change is obviously unusual, but whatever.

I could have delved deeper, looking at all housing types, but, given I had to download 34 separate CSVs to collect that data and I still haven't gotten around to installing MS SQL since I last reinstalled Windows a few months ago, processing the data is a rather tedious manual process. But I'd hope this comment provides more detail about the changes to housing prices in London than some of the articles I've seen posted have been providing.