London's private rented sector is contracting at a pace that should alarm anyone tracking the capital's housing supply. New data pointing to a sustained landlord retreat from the London market confirms what many letting agents have been reporting anecdotally for months: available rental stock is tightening sharply, even as tenant demand remains resilient. This is not a cyclical blip. It is the visible outcome of a multi-year squeeze on buy-to-let economics that has finally reached a tipping point in the country's most expensive, most heavily regulated rental market.