I mean, you can match those Barcelona prices in nice market towns a short train ride from central London (probably a similar door to door time to many parts of central London to commuting from West Hampstead), which many London workers actually do. They can think about buying in those areas from £75k as well.
But the investment bubble at the high end of the property market is a largely separate phenomenon; middle-class renters are more likely to take advantage of cheap rents from a lazy letting agent managing the investment property of a foreign owner who's not too savvy about what their buy-to-let income should be than they are to be affected by the unoccupied flats in Belgravia not being on the market. For that reason, for £28000 a year I got five large bedrooms, two reception rooms and a garden in a desirable south London suburb three years ago, so I'd expect a pretty impressive[ly located] 2 bed flat for £25000....