text: Nearly four-fifths of the RCN members surveyed were worried about the cost of their accommodation.
  The RCN's London regional director said essential services were at "breaking point".
  Last year 17% of all London's registered nursing jobs were vacant.
  Ben Morrin, the director of workforce at University College London Hospitals NHS Foundation Trust, told the BBC that hospitals initially offered subsidised accommodation to new staff.
  King's College Hospital offers rooms in shared accommodation for Â£452 per month, including bills and council tax.
  A nurse's starting salary (including 20% inner London weighting) is Â£26,030.
  But as staff settle down they are tempted by the lower cost of living outside the capital.
  "Normally we get to a decision point after two to three years when they want to move outside the capital, and the reputation of London's teaching hospitals makes it easy for them to find jobs," Mr Morrin said.
  "We have trouble in retaining those nurses."
  One agency specialising in accommodation for NHS workers offers a single-bedroomed flat in Limehouse, east London for Â£1,350 - over three-quarters of take-home pay on a starting salary.
  "With staffing shortages in London getting worse by the year, while patient need continues to go up, essential services are being stretched to breaking point," said Bernell Bussue, the regional director of RCN London.
  The college is calling on the next London mayor to offer discounted travel for NHS workers, and require new homes built on NHS land to be offered first to low-paid NHS staff.
  Source: NHS Employers
target: Four in 10 London nurses expect to leave the capital by 2021 because housing costs are so high, according to a survey by the Royal College of Nursing (RCN).