Reliable sources on house prices in the UK/London

I can't help feeling (based on this and your previous questions on similar topics) that you are going about things the wrong way.

There is a website that provides individual sold house price data: https://nethouseprices.com/ which lets you search down to the "first half of postcode" level, but how can you tell from that whether "house prices are going up or down"? You can't, because if you see that property A sold for £X and property B sold for £X+Y, you don't know whether property B is equivalent to property A or not - larger property, better condition, better amenities, or even just the owners had a better estate agent who was able to negotiate a better price.

The reason you read conflicting information is because there are different kinds of analysis you can do on the raw data - is the mean house price rising/falling? or the median? or the maximum price paid in the area? or the mean / medium / maximum amount above original asking price? or the spot price of some kind of house that the analyst has decided is a "typical house" in this area? These signals could be going in different directions and different analysts will decide that different ones are more important (or more likely to generate a news headline that will get clicks / views).

So let us say you want to do your own analysis and so you devote your life for a year or two to collecting data and going round on foot and meticulously comparing the details of the properties that you have sold data for. Great, now you have a really accurate pile of information about what has happened over the last period of time (however long you've been collecting it for). What does that tell you about what will happen to house prices tomorrow, or next week, or next month, or next year? Nothing at all.

It sounds to me like in an effort to compensate for your lack of experience of the housing market in general, you are trying to focus on pinning down various pieces of data in a way that really isn't helpful or even possible.

My advice would be: decide from your own life circumstances right now whether buying (vs renting or living with family) makes sense. If buying makes sense, work out your own budget to determine what you can afford (including if interest rates rise substantially). Look at the types of house you can afford in the area you want and decide whether that is acceptable to you. If not, look at smaller / cheaper houses, or less expensive areas.