Thames Reach Bondway is warning local authorities of an inevitable rise in street homelessness unless they create more homes for long-term hostel residents.
The homelessness charity has sent 2,000 posters to central and local government representatives and its own supporters. They show a listing page for accommodation in London with every entry crossed out, alongside the headline 'No Vacancies'.
The tactic draws attention to the near-impossible task for charity staff of placing hostel residents in suitable settled accommodation.
The charity said a bottleneck had developed because of a lack of available permanent accommodation in London. This meant that previously homeless people were unable to move on from stays in hostels, which are supposed to last less than a year. This, in turn, has left homeless people unable to access hostels, where they should be readjusting to life off the streets.
The charity claims that if London's 33 boroughs give 10 flats each to a pool of accommodation for people stuck in hostels, 330 people could move on and free up beds for those living on the streets.