Toddler, interesting post, and I agree that it is more than supply and demand, but that is the very crux of the "bubble" anti bubble argument which should be better explained.
The population of London fell from 1940 to about 1988 where it was at about 6.8 million, the house prices were slightly more expensive due to the demand for housing being higher, but they were not too far away from the rest of the country.
Since 1988 we have seen the population start to rise again, to is current 8.5 million which is now back at the pre war high. So actually there is a huge basic supply and demand issue here, the increase in population creates more demand than there is supply of housing forcing prices up.
Secondly since 1939 we have seen a huge societal change in the way that households exist. We have more single people who are property owners, more split families, also (and this is important) the role of women has changed, women who are unmarried do not stay at home with Mum and Dad these days, they have their own households. All of this creates more demand, but again the supply is relitively inelastic so this drives prices up.
The money people are able to borrow has changed too, way back when my parents first got their mortgage it was 2.5 times by Dad's salary, my Mother's income was not taken into account. These days both incomes are taken into accout and the amount you can borrow reasonably seems to be about 4 x both. This drives prices up too! The credit controls of the last 5 years (no more 100% mortgages etc) have done little to stem the demand for London property.
This next bit is important, the pool of waiting entrants to the market keeps prices high. This thread is the very evidence of it. If prices were to fall ever so slightly, lots more consumers would be able to purchase housing, this acts on the market by the fact that if you drop the price for the flat a little, two or more people are bidding on it, they raise their bids slightly in order to get it, which then effects the way the next flat of its type on the market is priced.
There are also limits on the kind of property a first time buyer can get a mortgage on. Nothing above commercial units, and nothing over the 4th floor of a block will get a mortgage. This increases the demand for the houses/flats that they can buy, which again then inflates the rest of the market.
This means that any short term slump in prices is counteracted (eventually) by the consumer themselves causing prices to rise.
The baby boom analogy you made is probably not quite correct either. It is unlikely that there would be a large enough glut of property onto the market at one time in order to force prices down, these properties are much more likely to be sold off across the next decade in a piecemeal kind of way, meaning that prices will remain relatively stable. I'd imagine many who have seen the value of their property escalate have already sold up, provided children with deposits ( thus causing rising prices) and downsized. Well there will be as many of this type of person as your theortical Aunty Doris who will be looking to sell her house in ten years time.
Back to the population point finally, the population is projected to increase to 10 million in the next decade, thats an extra 150,000 people a year coming into the city, again enhancing demand, and thus causing prices to either maintain or rise.
See the real problem is not rich oligarchs buying Chelsea property, or investment boxes in the sky, it is supply and demand, there are many deteriminants of that demand, but it really is that simple.