The London, south east England, further British popular sought after spots including many as mentioned up thread ie Cotswolds, Chilterns, Poole, Dorset Jurassic coast, Cornwall, Edinburgh, etc can be explained in terms of elementary economics as follows.
UK government policies in recent decades of all political viewpoints (but I consider Blair a classic hybrid red Conservative) always continue to ensure via housing policies, town and country planning and supply economics such as all the recent SDLT and first time buyer policies to target one major overriding objective. That unofficial objective is to ensure market stability but actually it is more deigned to favour perpetual housing (and land) asset value/pricing appreciation. All the government policies essentially (in my humble opinion as not an expert in real estate development economics) pander to and incentivise the all powerful (private of course as limited social or complementary paid for by others council housing) big house builders to supply new housing in a market where there forever a "deliberate" unbalanced equilibrium in housing stock supply and increasing demand. In London and these above sought after spots an unbalanced supply and demand market dynamic is just the market capitalists way we live in. Essentially as long as the house prices continue to rise above inflation (although inflation has been super low in recent times) and out perform other investment asset classes apart from specific limited supply commodities such as rare earths etc - "everyone" is happy. Of course what that means is renters (not by choice) lose out as they are forever priced out as the gap between local incomes and local house prices increase the unaffordability scale. Renting market heats up again due to limited supply and this high demand only means the "poor" renters are trapped outside of the property ladder and instead pay the mortgages of their landlords. Many of these landlords themselves being incidental originally having purchased property historically at legacy pricing levels and now enriched by asset appreciation and a decent additional income stream to perpetuate further buy to let market. UK mortgage debt market itself is weighted more towards buy to let as there is a more guarantee income stream to borrow more than for a regular owner occupier mortgage loan.
So limited house building but increasing demand (to buy and rent) with smaller household dynamics and the rise of the divorced or single parent demographic and net national and international immigration (to London and other economically prosperous spots) helps to increase demand and so increase the property market price further.
In addition to limited supply as big house building players and investors (UK pension funds and international investment vehicles/sovereign wealth funds and pension funds etc) play the market to their advantage. It's big business not charity as they need a safe and "guarantee" return on investment as a part of a diversified investment portfolio.
One must simply understand and appreciate the housing market food chain! In core central London leading the price per square foot/meter is UK aground zero market apex. I am of course referring to off market by invitation localities where a small elite market is prequalified to bid not the man/woman on the street unless big lottery winner perhaps. Naturally being a global investment store of value and dare I suggest (as a City professional) as it is generally agreed - we facilitate this legally with complex inventive taxation and investment vehicle structure strategies to optimise and pay the "legally correct taxation." This is a subtle difference from moral financial obligations from those ironically most able to pay and to pay for the best professional advice. So all the up thread posters who are displeased and displaced from being priced out of localities they wish to buy (or rent) will hopefully understand that London is a global safe investment residential and commercial property market. Richer Londoner are priced out by the global high net worth be it Chinese, Russian or Gulf States financial firepower. The priced out central Londoners then move further out to commuter territory eg Surrey and Hertfordshire etc. This is in turn trickle down to surrounding regions to sought after leafy market towns with the right mix of amenities and transportation links. The same in other sought after local hotspots eg Cotswolds, Cheshire professional footballer territory, Cornwall coastal villages, etc etc. It's just basic property market economics and the common factor is ensuring the land and property price remains high and appreciates. Look what happened with the USA residential market collapse in recent times as that essentially initiated the previous global economic recession. If the price sky rockets eg central London over recent decades then many owners are incentivised to either expand by building loft conversions or additional super basement super subterranean luxury spacious living or selling up with a big fat profit and buy a much larger property in a nice spot further out by pricing out the original locals. The return on this building investment is a no brainier when the return is a multiple of costs. That is why London is such a sought after safe international market. We have political stability compared to China, Hong Kong, Russia, Middle East etc and strong property protection laws as no government is suddenly going to be unstable by political coup or instantly change laws to compulsory purchase or as in many poorer undeveloped countries literally move the earth to take away your property and land without legal recourse to favour the corrupt elites. Hope this helps but then I am positive the mums of MumsNet know this stuff already!